The quake rocked Anar village, some 700 kilometres (400 miles) south of Tehran, ISNA said.
There were no immediate reports of casualties or major damage.
Iran is prone to earthquakes as it sits on many major fault lines.
On 5 April, a 6.1 magnitude quake killed at least two people near Iran's second city Mashhad, which is located southeast of Bojnurd.
In January, a magnitude 5.3 earthquake killed four people in the village of Saifabad near the town of Khonj, about 1,000 km south of Tehran.
The region is on an active fault line stretching from Turkmenistan's capital Ashgabat into Iran's three provinces of north, central (Razavi) and south Khorasan.
The last major earthquake to strike Iran was in 2003 at Bam, in the southeastern province of Kerman, which killed at least 26,000 people and flattened the city.
Agencies contributed to this report.