The Istanbul-based Kandilli seismology centre says the quake occurred at 8:49 p.m. (1749 GMT) Sunday. Its epicenter was in the Sea of Marmara.
The quake was felt in Istanbul, Turkey’s largest city.
Earthquakes are frequent in Turkey, which is crossed by faultlines.
In 1999, about 18,000 people were killed two powerful earthquakes that struck northwestern Turkey.