The quake struck at 1.58am on Saturday (1658 GMT Friday) in the Banda Sea, about 195km south of Ambon city in the Maluku Islands, the USGC said on its Web site. It occurred at a depth of 342km.
There was no danger of a tsunami, and no immediate reports of injuries or damage.
Internet news portal Detik.com reported from Ambon that people fled their houses in panic when the earthquake, which lasted about two minutes, struck.
The Pacific Tsunami Warning Centre said no destructive tsunami threat existed.
"Because this is a deep earthquake there is little possibility of a tsunami," an analyst at the National Earthquake Centre in Jakarta said.
Amran, an official at Indonesia's meteorological agency in the capital Jakarta, said there were no immediate reports of damage or injuries. Like many Indonesians he goes by only one name.
Ambon is about 2600km east of Jakarta.
Indonesia, the world's largest archipelago, is prone to seismic upheaval because of its location atop a volcanically active region known as the Pacific "Ring of Fire".
A magnitude 9 earthquake and subsequent tsunami on 26 December 2004,killed more than 131,000 people in Indonesia's western Aceh province on Sumatra island and left a half-million homeless.
Three months later another strong tremor killed more than 900 on Nias and smaller surrounding islands, also in western Indonesia.