Saada has been the site of an uprising by members of the Zaidi community, a branch of Shia Islam, that has killed thousands of people since 2004.
The fighters are known as Huthis after Hussein Badr Eddin al-Huthi, their former commander, who was killed by the army in September 2004.
The Huthis have been fighting to restore the Zaidi imamate, which was overthrown in a coup in 1962. Huthis blamed
The government blamed the Huthis for Friday's blast and said six people had been arrested.
"Those who carried out this ugly crime are terrorists and criminals linked to the terrorist Abdul-Malik al-Huthi," an interior ministry statement said, referring to the brother of the late commander.
However, the group has denied any responsibility.
Abdul-Malik al-Huthi told Al Jazeera: "We condemn this regrettable incident and deny categorically any role in this incident.
"It is not part of our ethics to target mosques or worshippers at all."
The renewed violence comes despite efforts to implement a peace deal between the government and the fighters, brokered by Qatar in June 2007.
The agreement, under which the fighters would lay down their arms, was revived during a meeting between the two sides in Doha in February.
In January, clashes renewed between the fighters and thousands of government troops backed by tanks, artillery and helicopters.
Tribal leaders in the northern region say more than 30,000 residents have been displaced by the fighting.
Speaking to Al Jazeera on Tuesday, Mohammad al-Qadhi, a political columnist for the Yemen Times, said that both sides continue to blame each other for the renewed violence.
"There seems to be groups within the two sides [government and Huthi fighters] that are ideologically fanatical and do not want to see the development of peace in the area," he said.
"What we have seen from the violence is that both sides cannot defeat each other, and the only option for them is to sit down and talk."
Source: Al Jazeera and agencies