Authorities said a stun grenade exploded at a metro construction site in Heliopolis on Saturday leaving no injuries.
Reports have not clarified whether the explosion was from an actual grenade or merely a homemade bomb.
The bomb was found near the Ramses College for Girls by one of its workers who was later taken to an ophthalmology hospital for checkup.
Egyptian provinces have seen an increase in the use of bombs and stun grenades since the ouster of former president Mohamed Morsy. Authorities blame the attacks on the Muslim Brotherhood and extremist groups loyal to the deposed leader.
Edited translation from Al-Masry Al-Youm
