Three other service members were hurt, the Nato alliance said. The explosion occurred near Bagram air base, 50km (31 miles) north of the capital Kabul.
Earlier three people were killed in twin explosions in the eastern city of Jalalabad.
A total of seven US military members have died in Afghanistan in 2019. In March, two soldiers were killed.
The US has about 14,000 troops in Afghanistan.
In February, the top US envoy seeking to broker peace in Afghanistan met the Taliban's co-founder in an attempt to end the 17-year conflict.