The bombing occurred after a day of clashes between opponents and Islamist supporters of Egypt's deposed president, Mohamed Morsi, killed nine people in Cairo.
The Muslim Brotherhood, which propelled Mursi to power in the country's first democratic elections in 2012, accuses the army of orchestrating a coup that has exposed deep political divisions in the Arab world's most populous nation.
Supporters of Morsi, who has been held in an unknown location since the army deposed him on July 3 following mass protests calling for his removal from power, have vowed to stay in the streets until he is reinstated.
About 100 people have died in violence since the army deposed Morsi and replaced him with an interim administration led by Adli Mansour, the head of the constitutional court.New elections are expected to be held in about six months.
In the latest bout of violence in the capital, two protesters were killed at a pro-Morsi march early on Wednesday after clashes in Cairo, a security source and the Muslim Brotherhood said in a statement on their website.