Security officials said paramilitary troops on Monday ordered the explosives-filled Toyota Corolla station-wagon to stop as it neared a roadblock 6km east of Miranshah, the main town in the area. The driver then detonated his bomb.
Five soldiers who had been washing outside a mosque near the checkpoint, were injured, an official said. Military helicopters airlifted them to hospital.
All roads in the area were closed off after the attack.
The attack, on Monday, came the day after an insurgent commander said a month-long ceasefire had been called to give tribal elders time to negotiate a settlement to end the conflict in the semi-autonomous region.
Abdullah Farhad, a purported spokesman for the fighters, in telephone calls to local newspaper offices, said the ceasefire is "conditional, if the security forces attack us then we reserve the right to defend ourselves".
The fighters also gave a string of demands, including replacing army troops with tribal police; keeping soldiers in their barracks for the period of the ceasefire; and the release of all tribesmen detained in military operations.
Ali Jan Orakzai, a spokesman for the governor of the North West Frontier Province, said: "We welcome the announcement of a unilateral ceasefire."
About 80,000 Pakistani troops are in the region looking for Taliban and al-Qaeda fighters who crossed the border from Afghanistan after the fall of the Taliban government in 2001.