At least one person was killed when a primitive bomb exploded after being thrown at a police vehicle near a metro station in Giza, deputy Giza security chief Mahmoud Farouk told state TV.
TV footage showed a police cordon around El-Behous metro station in Giza's Dokki district.
At least 11 others were reportedly wounded in the attack.
Earlier on Friday, a major blast hit a Cairo police headquarters, killing at least four and injuring 51 others
Bomb attacks have become commonplace since the ouster of president Mohamed Morsi in July, but until Friday deadly attacks have largely taken place outside the capital.