The Sea-Based X-Band Radar-1 left Hawaii about a week ago to conduct routine systems checks at sea, according to the U.S. Navy.
Some Hawaii residents affectionately call the radar, the "golf ball."
However, a CNN report cites a Defense Department official saying that the SBX-1 is moving closer to the North Korean coast to monitor that country's military moves, including possible new missile launches.
The defense official also says the USS John S. McCain is moving closer to North Korea in the first of what may be other naval deployments.
This comes after weeks of rhetoric from North Korea talking about threats of using nuclear weapons.
The U.S. has also added flights of B-2 stealth bombers, B-52s and F-22 Raptor stealth fighters near North Korea.
The SBX-1 is a radar that is able to track ballistic missiles and provide data to interceptor missiles so all threats can be successfully destroyed.