The epicentre of the quake was in Khuzdar city - about 300 km from the provincial capital Quetta - at a depth of 26 kilometres.
Officials said there was no loss of life or property due the tremor that struck late morning and was felt in surrounding areas.
Pakistan lies in the active seismic zone and often experiences quakes.
Last year, a 7.7 intensity tremor struck the province, killing more than 500 people.
In 2005, a 7.6 magnitude quake had killed nearly 74,000 people, rendered about 3.5 million homeless and devastated several cities in the north.
