Officials said the bomber drove his car, packed with explosives, into a crowd of policemen in the regional capital of Oruzgan Province, Tirin Kot. It is unclear how many of the victims were police and how many were passersby.
The attack occurred some 500 meters from the provincial governor's headquarters.
A local government spokesman, Abdullah Jan, said the governor was not present. He is in Mecca for the hajj pilgrimage.
The number of suicide attacks in Afghanistan have increased in recent months, with insurgents vowing to step up their use of the tactic.