Georges Zicot is the seventh person to be arrested since the scandal first came to light almost two weeks ago.
Police did not implicate him in child abuse but said he was an associate of the chief suspect, Marc Dutroux, who has admitted kidnapping and abusing children.
The Public Prosecutor, Michel Bourlet, said: "Georges Zicot was arrested and will be charged with truck theft, insurance fraud and document forgery."
Mr Bourlet added that two other people had been arrested and that there had been a search of the judicial police headquarters in Charleroi, the southern Belgian town near Dutroux's home. He said one of the other two arrested was the owner of a warehouse where stolen vehicles were allegedly stored. The other was an insurer.
Mr Bourlet said an investigation into a vehicle theft ring would be added to the inquiry into the paedophile sex scandal. Another four people were questioned at the weekend but were not detained, he added.
The child sex scandal first became public when two teenage girls were rescued from a sound-proof cellar where they had been imprisoned, one of them for three months.
Their discovery gave police hope that two other missing teenage girls, who vanished from Ostend a year ago, might also be found alive.
The two men at the centre of the paedophile investigation - Dutroux, an electrician and convicted child rapist, and Michel Lelievre, his associate - have admitted kidnapping the girls.
However, the gruesome discovery of the bodies of two more young girls just over a week ago in the grounds of a house owned by Dutroux in the village of Sars-la-Buissiere, concentrated the police effort. Police confirmed the two girls had starved to death.
In The Netherlands, police in acting on a tip-off held a 74-year-old Dutchman in connection with the Belgian scandal. Two firearms were found in his house in Amstelveen near Amsterdam.
The child sex scandal has rocked Belgium. There have been angry scenes and public outpourings of emotion throughout the country as its population tries to come to terms with the tragedy.