Senior police officer Akhtar Hayyat said several people were also wounded in the blast near a gas station in the district of Buner in the Khyber Pakhtunkhwa province. He said Fateh Khan, the head of the local anti-Taliban militia, was killed along with three guards and two passers-by.
Khan was also a prominent leader of the secular Awami National Party, which rules the coalition government in the province, and which has angered the Taliban by supporting several military offensives in tribal districts and in the towns.
Shortly after the attack, Taliban spokesman Ahsanullah Ahsan claimed responsibility by telephone for the killing of Khan.
Buner is believed to be a hiding place for the Pakistani Taliban. It is located near the Swat Valley, where the insurgent group shot and wounded 15-year-old education activist Malala Yousufzai last month for criticizing its behavior when it seized the isolated region in 2008.
An offensive by the military broke the Taliban's control over the area in 2009, but attacks have continued.
Associated Press Writer Rasool Dawar contributed to this report from Peshawar.