A security official, speaking on condition of anonymity because he was not authorized to speak to journalists, says 4 of the people injured on Saturday are police officers who were guarding the entrances to Cairo University.
The official says the blast went off by a subway entrance near the campus. Security officials have cordoned off the area and are sweeping for additional explosives.
Egypt has faced regular militant attacks, mostly targeting security forces, since the military's ouster of elected Islamist President Mohammed Morsi in 2013. Militant groups say they are avenging a security crackdown on Islamists, while authorities blame Morsi supporters for the violence.
Related story
Egyptian officials say 55 police killed in Cairo shootout
