Some earlier reports said people had been killed in the explosion in the central commercial district of Kizilay, BBC reports.
Turkey's deputy prime minister said "there is information that a bomb was planted" on a vehicle.
A bomb squad was sent to the area of the blast and firefighters contained a fire.
Several parked cars outside the local state authority's officers were ablaze and windows were blown out in nearby buildings, BBC reports.
Kurdish, leftist and Islamic militants have carried out bomb attacks in Turkey in the past.
A local TV station reported that the explosion occurred in a minibus, Reuters reports.
Dogan News Agency quoted police sources as saying the blast was caused by a bomb and fire service officials as saying that two people had died. It also reported that police had detained a woman near the scene.
Cankaya Mayor Bulent Tanik said nobody was killed but three people had been seriously wounded, while broadcaster CNN Turk said 20 people were wounded and were being treated at three hospitals.