Mohamed Ben Khalifa, who was in his 30s, was hit by shrapnel while accompanying a military force that is raised from the civil population to supplement a regular army in an emergency in the Qaser Bin Ghashir area, south of Tripoli.
The militia came under attack by another armed group. He said there was gunfire, and that a missile was also fired.
Ben Khalifa, a photographer and video journalist, is survived.
A new round of fighting between rival militias erupted earlier this week, killed13 and wounded 52 people, Libyan Health Ministry reported.