Several Islamist fighters belonging to the country's most active militant group, Ansar Beit Al-Maqdis, have been arrested.
A security source told state news agency MENA on Friday that they were among the suspects in the killing of a female journalist.
Mayada Ashraf, 22, was shot dead in Cairo on 28 March while reporting on clashes between police and Islamists.
Journalists have repeatedly complained of being targeted by the police and supporters of ousted Islamist president Mohamed Morsi while covering clashes.
Ansar Beit Al-Maqdis, or Supporters of Jerusalem, has claimed responsibility for many of the deadliest attacks -- which have killed 500, mostly police and troops -- since the ouster of Morsi last summer.
These include a failed attempt to blow up the interior minister last September, and high-profile car bombings of police headquarters.
The suspects were arrested in raids on hideouts in shacks north of Cairo, near and in Qalyoubiya governorate, the official said.
Both Egypt and the United States this month designated Ansar Beit Al-Maqdis a terrorist group.
The group, which emerged in 2011 after the ouster of president Hosni Mubarak, launched attacks on neighbouring Israel before switching its focus to Egyptian police and soldiers following Morsi's removal.
Dozens of Islamist fighters have been killed and hundreds arrested as part of an ongoing offensive in the Sinai Peninsula to combat a growing insurgency.