No damages were reported after the quake struck, centered in Bolu's Yeşilcele at 00.16 a.m local time, at a depth of 7.2 kilometers (4.4 miles), the agency said.
Experts believe the frequency of the earthquakes could trigger a bigger tenor that would hit Turkey's northwestern Marmara region, including the densely populated city of Istanbul.
Geologists and authorities say, however, Istanbul is not prepared for a major quake, an event experts in recent years have warned could occur at any time.
A magnitude-7.4 quake hit the industrialized town of Izmit in western Turkey on Aug. 17, 1999. Istanbul, located just 49 miles (80 kilometers) east of Izmit-was badly affected by the quake that was the deadliest in Turkey in 60 years.
Approximately 18,000 victims were killed in the disaster and nearly 50,000 others were wounded.