At least 30 others were also wounded in the incident, which took place in eastern Laghman province's capital, Mehtarlam, Afghanistan's interior ministry said on Monday.
The condition of the governor, Rahmatullah Yarmal, was not immediately known and officials would not confirm local reports that he was slightly wounded in the bombing. Yarmal escaped unharmed, a provincial police spokesperson said.
Interior ministry spokesman Tariq Arian said four of Yarmal's bodyguards had been killed in the bombing. He said the wounded included 28 civilians and two other guards.
No group has claimed responsibility for the incident. Both the Taliban and ISIL (ISIS) armed groups are active in the area.
The Taliban group has carried out assassinations of high-profile Afghan officials recently, while both groups attack government representatives, national security and defence personnel as well as civilians.