The tremor on Tuesday followed a pair of offshore quakes in the same area earlier Tuesday, including one that was magnitude 6.1 south of the city of Raba.
The latest one struck about 85km south of the town of Kahale, according to the United States Geological Survey.
There were no immediate reports of damage or casualties.
Disaster-prone Indonesia, which sits on the geologically active so-called Pacific Ring of Fire, where tectonic plates collide, suffered its deadliest year in more than a decade in 2018 as a series of earthquakes and tsunamis killed thousands of people.
The vast Southeast Asian archipelago of more than 17,000 islands is still reeling from a devastating tsunami at the end of December triggered by an erupting volcano in the middle of the Sunda Strait between Java and Sumatra islands that killed more than 400 people.
The tsunami was Indonesia's third major natural disaster in six months.
It followed a series of powerful earthquakes on the island of Lombok in July and August and a quake-tsunami in September that killed around 2,200 people in Palu on Sulawesi island, with thousands more missing and presumed dead.