Reports said that buildings in the provincial capital, Xining, were shaken but no damage was reported.
China's state-run Xinhua news agency said some mud houses near the epicentre had cracks in their walls and several huts had collapsed, but there were no reports of injuries.
Several schools in the area were closed as a precaution, the agency said.
In May a magnitude 7.9 earthquake hit the southwestern Chinese province of Sichuan, killing at estimated 70,000 people and flattening scores of towns and villages.
Many of the dead were children, buried under the rubble of collapsed school buildings.
Many parents of the dead children have complained that the schools were built of substandard materials or by contractors who cut corners and ignored building safety regulations.