A suicide bomber drove into a school in northern Yemen's al-Jawf province where members of a Shi'ite Muslim rebel group had gathered for Friday prayers and killed 12 people, the defence ministry said.
A local official said several people were wounded in the attack. The province borders oil giant Saudi Arabia.
Western and Gulf Arab states have watched with mounting alarm as al-Qa'ida-linked militants have exploited political instability in Yemen to gain a foothold there.
On Monday a suicide bomber dressed in army uniform blew himself up in the middle of a military parade rehearsal in the capital Sanaa, killing more than 90 soldiers and wounding more than 200 people. An al -Qa'ida affiliate claimed responsibility.
Washington is trying to counter the threat by deepening its involvement in Yemen, using drone strikes to target suspected militants and training the Yemeni army to fight them.
Earlier today, another suicide bomber targeted a Houthi protest march in the rugged northern province of Saada, where the rebels have effectively carved out their own state within a state. There were no casualties in the attack, the Houthis said in a statement.
"As the march was taking its first steps, the suicide bomber, who was wearing an explosive belt, tried to breach the security barriers and enter the square," read a statement from the Houthis' media office.
"But those responsible for protecting the protest stopped and searched him, which made him nervous and he lost control, blowing himself up erroneously..."
There was no claim of responsibility for either of today's attacks. Sunni Muslim militants affiliated to al-Qa'ida view Shi'ite Muslims as heretics.
The Houthis have fought regularly with Sunni Muslim Salafis attending a religious college in Saada. They accuse Riyadh of smuggling weapons to the Salafis because the two follow a similar creed.
Saudi Arabia briefly fought the Houthis in north Yemen after they grabbed Saudi territory in 2009.
The US envoy to Yemen said February there were signs that Shi'ite Iran was becoming more active in Yemen and could pose a deeper threat to its stability and security. Iran denies interfering there.