At least 37 people were wounded in twin bomb attacks on the small mosque in the Majouri district of Libya's second city during Friday prayers. The devices appeared to have been detonated remotely.
Two weeks ago, at least 35 people were killed by twin car bombings near another mosque in Benghazi.
Benghazi was at the center of three years of fierce fighting between extremists and forces loyal to Libyan military strongman Khalifa Haftar, who declared the city liberated last year.
Haftar heads a government based in eastern Libya, while an internationally recognized administration has been set up in the western capital of Tripoli. The western government has struggled to assert its authority across the country.
The uncertainty in Libya has opened the door to terror groups such as the Islamic State to set up camps.