At least six people were wounded early on Thursday in a car bombing near a state security building and courthouse in a Cairo suburb, security sources said.
The sources, who inspected the site of the blast in Shubraal-Khaima, said there was a burned-out vehicle and crater.
Comments on Twitter indicated the blast was heard in several parts of the Egyptian capital. Shopkeeper Mohamed Ali said he saw a man park a vehicle that exploded after he stepped away from it.
Militants based in the Sinai, who support the Islamic State group that controls parts of Iraq and Syria and have a presence in Egypt's neighbor Libya, have previously claimed responsibility for attacks on security forces.
Hundreds of soldiers and police have been killed since the army toppled Islamist President Mohamed Mursi in 2013 after mass protests against his rule.
Egyptian President Abdel Fattah al-Sisi has vowed to eradicate militancy, which he has said is an existential threat to the Arab world and the West.
Egyptian authorities have mounted the toughest security crackdown against militants in the country's history, drawing criticism from human rights groups who accuse the government of stifling dissent.
This month Sisi approved an anti-terrorism law that sets up special courts and protects its enforcers in the face of a two-year-long Islamist insurgency that aims to topple his government.
The law has come under fire from human rights groups that accuse Sisi of rolling back freedoms won in the 2011 uprising that toppled autocrat Hosni Mubarak.