Police Chief Zeki Catalkaya said no one was killed or injured in the explosion, which took place in front of an HSBC branch in the city on Wednesday.
Explosives experts are investigating the area around the blast.
A witness on the scene, Ramazan Elmaz, saw people crouching following the blast and had earlier said two people were injured, but later said that only one person was very lightly injured by broken glass.
The cause of the blast was not yet known, Catalkaya said.
HSBC's Istanbul branch was among targets hit by a series of suicide attacks in 2003 which killed more than 60 people.
Responsibility for that attack was claimed by a group linked to al-Qaida.