The guards were employed at America's largest base in Afghanistan. The ambush comes as Washington appears set to boost its troop presence in the country in a bid to tackle an escalation in the Taliban insurgency.
Gunmen have killed eight Afghan guards working at the largest American base in Afghanistan, officials said on Tuesday.
The guards were ambushed near Bagram base north of Kabul as they were driving home in a convoy late Monday, district governor Abdul Shakoor Quddusi said.
Quddusi added two other guards were wounded. "They were all local residents serving as guards at Bagram," he said.
The Taliban claimed responsibility for the attack.
US military in Afghanistan
US troops in Afghanistan now number about 8,400, and there are another 5,000 from NATO allies, a far cry from the US presence of more than 100,000 six years ago.
They mainly serve as trainers and advisers.
But Washington is soon expected to announce an increase in the US military deployment to bolster Afghan forces.
American military commanders in Afghanistan have requested thousands of extra boots on the ground.
Bagram, around 50 kilometres north of Kabul, houses the largest contingent of US soldiers in the country.
The ambush followed Saturday's "insider attack" in which seven American soldiers were wounded when an Afghan soldier opened fire at them inside a northern military base. Such attacks are expected to increase this year according to analysts as US troops engage with the Afghan military to double the size of its special forces.
The Afghan conflict is the longest in American history, with US-led forces at war since the Taliban regime was ousted in 2001.