"A remote-controlled device planted on a motorbike parked on the roadside went off when a vehicle owned by Malik Habibullah, a local pro-government elder, passed by," local police chief Sajjad Khan told AFP.
He said Habibullah was not in the car when the bomb exploded. Six people were killed and 11 others wounded, Khan said.
Pakistani troops have for years been locked in deadly battles with domestic insurgents in parts of the northwest.
The United States has in the past accused Pakistan of not doing enough to crack down on the militants, who also plot attacks on Western targets in neighbouring Afghanistan.
Elsewhere in the northwest, two policemen were killed while defusing a bomb in the district of Swabi, 50 kilometres northwest of Islamabad, police said.
"The two policemen had already defused four bombs planted near a government boys' school in the area but a fifth bomb exploded while being defused, killing both of them," local police chief Mian Muhammad Saeed told AFP.