At least 16 others were wounded in the incident in Rostaq district, council member Azam Afzali said.
No group immediately claimed responsibility. However, the ‘Taliban’ has vowed to do anything to sabotage the parliamentary election set for October 20.
The bomb was placed in a motorbike and exploded as the candidate was preparing to deliver a speech to supporters, Afzali and another provincial council member, Abdul Mahbob, said.
There were conflicting casualty tolls, with Mahbob saying nine were killed and 40 wounded.
This is the third such attack to have taken place in recent days.