The blast, which left more than 40 injured, took place at a marketplace in Khar, a town in the Pashtun tribal district of Bajaur near the Afghan border.
At least three policemen were killed in the attack, Reuters reported, citing local government officials. A BBC report puts the number of dead tribal policemen at five.
According to the BBC, a local Taliban group said the target of the attack was a security forces commander who was responsible for the deaths earlier of two insurgents.
The Bajaur district has witnessed a series of military offensives against the Taliban-linked militants in the past. Friday's attack took place after the authorities repeatedly said the area was secure, and it raises questions about the effectiveness of Pakistan's war against the deadly Taliban.
The BBC said the bomber walked up to the police checkpoint at a crowded market and detonated explosives attached to his vest. Most of the dead were bystanders.