Out of the eight injured in the blast near the Cairo University, four police officers and a conscript were in critical condition, a security official said.
The policemen were on duty guarding the university.
Additional security forces have been deployed at the blast site and the injured have been admitted to an area hospital, he said.
Egypt has witnessed several violent attacks targeting policemen, military personnel and civilians since the January 2011 revolution that toppled ex-president Hosni Mubarak.
More than 500 policemen and soldiers have been killed in the attacks since then.
The military has been conducting security campaigns in the restive areas, arrested suspects and demolished terrorist bases, including tunnels leading to the Gaza Strip.