"We are making thorough preparations to restart" the facility, he said. He did not say when it would be running again.
The White House had no immediate reaction on the North Korean plans.
Hyun spoke before the start of talks at the border village of Panmunjom with South Korean officials on sending energy aid to the impoverished North amid a deadlock in the six-party disarmament talks.
A landmark 2007 pact - made with the United States, China, South Korea, Russia and Japan - called on Pyongyang to give up and disable its nuclear program in exchange for the equivalent of 1 million tons of energy aid and other benefits.
Tension on the Korean peninsula has been high since the North stopped disablement work at its main nuclear complex on Aug. 14 in protest over Washington's failure to remove the North from its list of terrorism-sponsoring countries.
The U.S. promised to remove North Korea from the terrorism list after it declares its nuclear programs, which Pyongyang did in June.
Washington argues the communist country should stay on the list until it agrees to an international inspection system to validate its declaration.
North Korea responded by putting a halt to the disabling process and is now "proceeding with works to restore (Yongbyon) to its original status," Hyun told reporters.
The two Koreas are still technically at war because the 1950-53 Korean War ended with an armistice, not a peace treaty.
