There were no reports of property damage following the earthquake.
According to the agency, tremors were detected at 19:06 local time (10:06 GMT), with the focus at approximately 40 kilometers (25 miles) below the surface.
The quake was felt in other parts of Japan, including Tokyo and Fukushima.
Ibaraki prefecture is located on Japan's eastern Pacific coast, bordering Fukushima prefecture to the north. The prefecture, with Mito city as its capital, has a population of approximately 2.8 million people.