Unidentified gunmen opened fire following the blast that hit the Frontier Constabulary (FC) vehicle on Qambrani road in provincial capital Quetta.
Senior police officer Imran Qureshi said the bomb was installed on a motorcycle which was parked on the road where the FC vehicle had to pass through.
Police and paramilitary troops were called in the area to bring the situation under control.
Insurgents and militants in recent days have intensified attacks against security forces and national installations in Baluchistan, plagued by an insurgency and growing sectarian killings for more than a decade.