Two soldiers with suspected links to the Taliban fled and joined the insurgents after carrying out the attack overnight, said Sher Aziz Kamawal, a senior police commander in Kunduz, Reuters reported.
The outpost was among many forming a protective ring around Kunduz, which was briefly captured by the Taliban a year ago, the first time the movement had seized a provincial capital since losing power in 2001.
Insider attacks have plagued both Afghan and international military forces in the country, undermining trust and morale.
The Afghan government forces are battling various insurgent groups, including the Taliban, who say they are fighting to expel foreign troops and reestablish a fundamentalist regime.