A blast outside a court in Cairo's Heliopolis neighbourhood left three injured on Monday, a security source told Aswat Masriya.
The injured are a traffic police director, a policeman and a passerby, all of whom have been hospitalised, the source added.
The area is being combed to make sure there are no more explosives.
Militancy inside Egypt has surged since July 2013. While the vast majority of bombings and shootings take place in North Sinai, other parts of the country have been affected too.
In June, Egypt's top prosecutor was assassinated after a bomb hit his motorcade in Cairo.
The High Court Building in central Cairo, which hosts the top prosecutor's office, was targeted in March. A bomb exploded in front of the main gate of the building, killing two and leaving nine injured.
