A bomb exploded near a mosque in Giza on Thursday morning, no causalities were reported, security sources told the state news agency MENA.
The bomb squad moved immediately to the area of explosion to see whether it was caused by a terrorist act or not.
Another one exploded a few hours before dawn outside a military hospital in Abassia, there were no injuries reported, a security source said.
Unidentified assailants threw two makeshift bombs at police stations in the same district, earlier on Thursday, but they did not explode.
The explosions came to mark the first anniversary of the military's ouster of President Mohamed Mursi of the Muslim Brotherhood last year, which was prompted by mass protests against his rule.
A string of explosive devices blew up in Cairo earlier this week. Two policemen were killed while trying to defuse makeshift bombs on Monday outside the presidential palace.
The army closed down Tahrir Square and all the roads leading to it on Thursday to cars and pedestrians for security measures.
