The quake was centered in the town of Lixurion, on the Ionian island of Cephalonia, the U.S. Geological Survey said.
Lixurion is a coastal resort area outside the island's main town of Argostoli.
Ekathimerini.com said the tremor was felt as far away as Athens. The report said the European-Mediterranean Seismological Center pegged the quake's magnitude at 5.7.
There were no immediate reports of any damage or injury.