The 5:08 a.m. quake was the second to hit the island in eight days, ekathimerini.com reported.
The epicenter was located about 7.5 miles northwest of Argostoli, the Geodynamic Institute in Athens said. The largest aftershock measured 4.5 magnitude.
The injuries reported were minor, caused mostly by falling objects, said Dionysis Markatos, director of Lixouri hospital.
A 5.8-magnitude quake shook the same area Jan. 26, EnetEnglish.gr reported.
"We're talking about the same seismic area. In fact, the center of today's earthquake is just to the northwest of last Sunday's quake, [7.5 miles] from Argostoli, near the shoreline," said Dimitra Saplatzi, the institute director.