The attacker detonated the explosives strapped to his body outside the governor's house in the town of Zaranj as people were coming to work, said Maluang Rasooli, the provincial deputy governor.
The attack happened a day after the authorities recovered the bodies of five Afghan policemen who were tortured by the Taliban.
The five officers had their hands and legs slashed and their mutilated bodies hung from trees in a warning to villagers against working with the government, Juman Gul Himat, the provincial police chief, said.
The officers had been abducted two months ago from their checkpoint in southern Uruzgan province, Himat said.
"The Taliban told the people that whoever works with the government will suffer the same fate as these policemen," he said.
"This village is under Taliban control. There are more than 100 Taliban in this village."
More than 6,000 people have died in violence in Afghanistan this year - a record number, according to an Associated Press count based on figures from Western and Afghan officials.