The alliance did not provide more details, the Associated Press reported, saying an investigation was under way. It also did not disclose the nationality of the service member killed. NATO usually waits for member nations to provide those details.
The shooting is the latest in a series of deadly attacks on international troops by gunmen wearing Afghan uniforms.
In other violence, NATO says one of its service members died in a bomb explosion in eastern Afghanistan Sunday. No details on the attack were released.
Elsewhere in the country, two Taliban commanders and three insurgents were killed in fighting Friday with security forces. A NATO statement says one of the men was a senior Taliban commander who planned and organized roadside bombings and other attacks against Afghan and coalition forces throughout Faryab province.
The other, a subordinate commander, was a Taliban judge who attempted to impose Taliban law and punishment on civilians in the area.
The U.S.-led coalition routinely reports each time an American or other foreign soldier is killed by an Afghan in uniform, but the military is underreporting the number of overall attacks. The Associated Press reported earlier this month that the International Security Assistance Force, or ISAF, does not report attacks in which the Afghan wounds - or misses - his U.S. or allied target. It also doesn't report the wounding of troops who were attacked alongside those who were killed.
The number of such attacks have been on the rise. So far this year there have been 18 attacks killing 11 soldiers, compared to 21 last year killing 35 coalition service members, according to NATO figures.
That compares with 11 fatal attacks and 20 deaths the previous year. In 2007 and 2008 there were a combined total of four attacks and four deaths.
U.S. officials say that in most cases the Afghans who turn their guns on their allies are motivated not by sympathy for the Taliban or on orders from insurgents, but rather act as a result of personal grievances against the coalition.