The bomb, attached to a bicycle, was triggered by remote control when the vehicle of the commandant of Balochistan Constabulary was passing through Sariab Road in Quetta, police said.
At least eight persons were injured by the explosion, which damaged two rickshaws and a taxi.
However, the security official escaped unhurt.
Officials of the bomb disposal squad said the bomb had contained an estimated eight kilograms of explosives and ball bearings.
Security forces cordoned off the area and conducted a search operation.
No group claimed responsibility for the attack.
