Local health authorities said five women and four children were among the injured, the Afghan news agency The Khaama Press reported.
The Herat Police Headquarters said in a statement that a van exploded in the Haji Abbas area of Herat, prompting an investigation.
Intelligence officials said a magnetic improvised explosive device was attached to the vehicle.
So far, no group or individual has claimed responsibility for the terrorist attack.
It is the first deadly explosion in the Herat province after the Taliban regained power in the country in August last year, the source said.