Police said the bomb exploded near the vehicle carrying volunteers of the anti-Taliban militia in Upper Dir district of Khyber-Pakhtunkhwa province.
The injured were taken to a nearby hospital.
Officials said the incident occurred in the remote Dog Darra area and local residents faced difficulties in taking the injured to hospital.
They took the injured to hospital in private cars.
No group claimed responsibility for the attack though such incidents are usually blamed on the banned Pakistani Taliban.
The militants frequently target members of "peace committees" or anti-Taliban militias.
People in parts of Pakistan’s northwest have formed peace committees to support security forces against the militants.
The Taliban have killed hundreds of pro-government tribal elders and members of militias over the past few years.
Islamabad: Three members of an anti-Taliban militia were killed and seven more injured when a vehicle was targeted with a roadside bomb in northwest Pakistan on Saturday, police and witnesses said.
First Published: Saturday, July 21, 2012, 12:00