The official says the bomb was detonated today by remote control in Ghazni, the capital of the province of the same name.
Deputy provincial police chief, Col Asadullah Ensafi, says those killed included a police officer who was a criminal investigation director and a civilian.
He says three other civilians were wounded in the blast. No group has claimed responsibility for the attack.
Roadside bombings are a major threat to both Afghan security forces and civilians across the country.