The explosion also injured four Afghan soldiers and four translators, according to Afghan Defense Ministry spokesman Gen. Mohammad Zahir Azimi.
The Taliban claimed responsibility for the attack.
Azimi said the attacker approached on foot and detonated his explosives at about 7:30 a.m. at the base entrance.
"The attacker had the Afghan security force uniform on and that gave him the opportunity to reach the entrance to the base and carry out the attack," Azimi said.
NATO declined to release further information on the service members killed pending notification of their next of kin.