The tea factory is situated in Shizuoka city, NHK channel reported.
Shizuoka prefecture is one of the most famous tea producing areas in the country.
"The prefectural government confirmed the contamination on Thursday, detecting 679 becquerels per kg of radioactive cesium. The legal limit is 500 becquerels," NHK said.
The factory has now stopped shipping its tea.
The Fukushima plant was badly damaged by a powerful earthquake and following tsunami that hit Japan March 11. The plant operator has since been struggling to stop radioactive leak from the crippled reactors. Radioactive elements have been found in the water, air and food products in some parts of Japan.
Published 10 June 2011, 05:46 IST