Some of the demonstrators are carrying banners saying "God exists. No to terrorism".
At least 25 people died and 35 more were injured in an explosion outside St. Mark's Coptic Orthodox Cathedral in Cairo, Egyptian Health Minister Ahmed Rady said Sunday.
Copts are a large ethnic and religious minority in Egypt, making up between 6 and 10 percent of the population.
St. Mark's Coptic Orthodox Cathedral in the Abbassia district serves as the seat of the Coptic Orthodox Pope.