The latest explosion happened at a company in the Oaklands Business Centre in Wokingham just after 9am.
Two people suffered minor injuries in the blast.
Thames Valley Police said it was "likely" that an item of mail had ignited and caused the "small explosion".
South Central Ambulance Service, which covers Wokingham, said two men in their 30s were treated for blast injuries to their hands and upper bodies.
The service sent two ambulances to the scene after an emergency call came in at around 9am.
Fourteen workers were evacuated from the premises and were checked over by ambulance staff.
Ambulance spokesman Graham Groves said: "The paramedic teams treated two male members of staff, in their 30s, for blast injuries to their hands and upper body. However, their injuries were not considered serious and they did not need treatment in hospital."
The paramedic team remained on stand-by at the incident while police and fire teams conducted their investigation into the cause of the explosion, he added.
Police officers said it was too soon to say whether it was connected to yesterday's letter bomb attack at the offices of Capita in Victoria Street which left a woman with injuries to her hands and stomach.
The target for today's attack was not immediately clear, although there were claims that the company could be involved in speeding fines.
It is not thought to be another Capita office.
Thames Valley Police said: "Emergency services are dealing with a small explosion at a company in Oaklands Business Centre, Wokingham.
"Police were called to the incident by the ambulance service just after 9am today. Two people have sustained minor injuries.
"Police have evacuated the building and placed a cordon around the scene. An investigation has been launched, though it is likely an item of mail ignited and caused the injuries.
"We are aware of a similar incident in London yesterday but it is too soon to speculate as to whether this is connected."
A female employee at Capita, which runs London's Congestion Charge, required hospital treatment yesterday after after a letter bomb exploded in her hands.
The bomb, which was stuffed in a padded bag, detonated as she opened it in the post room at around 9.40am.
It is understood that the bomb was not intended for her. It was apparently addressed to someone specific in the company.
Scotland Yard's counter-terrorism unit is investigating yesterday's explosion.
A spokesman for the force said officers would examine whether there were any links between the incident and today's blast.
Army bomb disposal units surrounded the company, Vantis, which is part of a business park surrounded by other red-brick office buildings.
Two ambulances and a crew from Royal Berkshire Fire and Rescue Service were also at the scene.
Police taped off the road directly outside the building and evacuated staff but officers and other emergency services were still walking freely near the offices.
Vantis, the target of today's attack, is a specialist financial advisory company.
A spokesman for the firm would only confirm that there had been a small explosion at the Wokingham office and that two people had been slightly injured.
Workers in neighbouring offices were still at their desks as white-suited police prepared to enter the building to gather further evidence.
Employees from Lein Applied Diagnostics said they had heard nothing until the police and ambulance arrived.
They said they knew only that the company was a firm of accountants. They said they themselves made no special arrangements for the security of those opening mail and they suspected that Vantis was in the same position.
Employees of other companies gathered at the windows to watch the police operation but ambulance crews and the fire truck originally called to the scene were preparing to leave.
A spokesman for Vantis said the two injured men were shocked by the incident.
He said: "My understanding is that they are in a bit of shock, but their injuries have been dealt with on site."
He said the company has no direct involvement with speeding fines.
"We are not directly involved in any speeding fines or anything like that. We do not do any administration of such things. It is not our business.
"Our business is, we are accountants, tax and business advisers. We give advice to small businesses, that is what we do."
He said the company was "nothing to do" with Capita and did not have any involvement with Capita.
"I think it needs to be made clear that we act for lots of companies and lots of companies have their registered offices at our office, it is standard practice."
He said to his knowledge the package had not been targeted at Vantis.
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