The alleged explosive was discovered by three construction workers working on a parking lot about half a mile from derelict Fukushima power plant reactors, and a spokesman for the Tokyo Electric Power Company (TEPCO), the company that owns the plant, said the 85-centimeter (2.9 foot) long object is thought to be an unexploded bomb the US dropped during the war.
After the object was found TEPCO immediately called the authorities, roping off an area of roughly a kilometer near the reactors and suspending construction work.
The Fukushima Daiichi Nuclear Power Plant experienced a nuclear meltdown after it was damaged by an earthquake that triggered a tsunami in Japan in March 2011. The meltdown was the worst nuclear incident since the 1986 incident at Chernobyl, in what is today Ukraine.
The discovery of the suspected bomb has not had any impact on decommissioning operations.
Although the war ceased more than 70 years ago in 1945, undetonated bombs and shells from the US are still found in Japan occasionally, especially on Okinawa, where a particularly intense battle took place in the closing months of the war.
According to Newsweek, a little over 900 unexploded munitions were found in Japan in 2010. In 2005, when a 2,000-pound bomb was discovered in Tokyo, 7,000 residents had to be evacuated.
The area around the site where the stricken Fukushima now sits was a key target for US bombing operations as a Japanese military airport was once located there, AFP reports.
Tens of thousands of people remain displaced as the Japanese government and TEPCO continue decommissioning and clean-up operations expected to span 40 years. Most of the people who left lived in Fukushima prefecture, where high radiation now makes habitation impossible.
Though no deaths have been directly linked to the Fukushima meltdown itself, TEPCO executives went on trial in late June for professional negligence that resulted in patients evacuated from a nearby hospital suffering injury or death. All three executives have plead not guilty.