The blast came as Egyptian security forces used tear gas to disperse small protests in Cairo on the anniversary of the popular uprising that ousted President Hosni Mubarak in 2011.
In a separate development on Saturday, a female protester was fatally shot in central Cairo near Tahrir Square, the symbolic heart of the 2011 uprising that put an end to Mubarak's 30-year rule.
Shaimaa al-Sabbagh of the Socialist Popular Alliance Party was reportedly killed as police were dispersing a protest in downtown Cairo.
On Friday, a 17-year-old girl was killed during protests in Egypt's second most populous city, Alexandria. The outlawed Muslim Brotherhood blamed security forces.
Police have repeatedly clamped down on the Islamist party's members since the army toppled Mubarak's successor Mohammad Morsi in 2013 after a year in power.
Hundreds of Morsi supporters have been jailed since then. The former president currently stands trial; he is charged with crimes including espionage and involvement in terror attacks.
