The blast took place at the office of Parisa Shams Sadat in Zari district of the province, provincial police spokesman Shir Jan Durani was cited as saying by Xinhua news agency.
All the victims were civilians. Villagers said the number of casualties was higher than reported.
The attack came a day after the provincial police chief and intelligence chief were assassinated by the Taliban.
The Taliban has vowed to "severely disrupt" the polls, in which some 2,500 candidates are running for 249 seats in the Afghan Parliament. Ten of those candidates have been killed in pre-election violence, along with more than 100 other Afghans.
The militant group said it will block roads to prevent voters from reaching the polling stations. The insurgents allege that the elections are aimed at legitimizing the presence of foreign troops in the country.
In recent months, Afghanistan has witnessed dozens of attacks on electoral workers and candidates.
According to the poll body, out of the 7,384 voting centres that fall in Taliban territory, 2,384 will remain closed on election day.
(This story has not been edited by Social News XYZ staff and is auto-generated from a syndicated feed.)
