The 6.1-magnitude hit 190 kilometers (115 miles) northwest of Bengkulu, the U.S. Geological Survey said on its Web site.
Although the temblor was felt in cities along Sumatra's west coast, it was not strong enough to cause a tsunami and there were no immediate reports of damage, said Nugrahani Farisa of the local Meteorological and Geological Agency.
Wednesday's tremor followed last week's 8.4-magnitude quake that killed 23 people along the western coast of Sumatra. More than 60 strong aftershocks have followed the massive earthquake - including a magnitude 7.8 and a 7.1.
A 10-foot-high tsunami was triggered by initial quake, but no one died from the wave.
Indonesia, the world's largest archipelago, is prone to seismic upheaval due to its location on the so-called Pacific "Ring of Fire," an arc of volcanos and fault lines encircling the Pacific Basin.
A massive earthquake and subsequent tsunami on Dec. 26, 2004, killed more than 131,000 people in Indonesia's Aceh province and left half a million homeless.