It says today's blast at St Mark's Cathedral in central Cairo wounded another 10 people.
St Mark's Cathedral is the seat of Egypt's Orthodox Christian church and is home to the office of its spiritual leader, Pope Tawadros II.
The agency says a bomb was lobbed inside a chapel that is adjacent to the cathedral's outer wall.
On Friday, six policemen were killed in a bomb attack in Cairo claimed by a group suspected by authorities of links to the outlawed Muslim Brotherhood.