The jet had taken off from a rebel-controlled airfield near the eastern city of Benghazi in the morning and was intercepted within minutes, the official said on condition of anonymity. No weapons were fired by either side.
"No aggressive action was displayed by the MiG-23 and the NATO fighters proceeded to force it to land back at the Benina airfield," the official said.
The official added that the rebels had not warned NATO that one of their jets was going to take off.
It was the first time that any aircraft violated the no-fly zone since NATO took command of the mission from a US-led coalition on Mar 31.
The UN Security Council put in place last month a no-fly zone over Libya to prevent Moamer Kadhafi from using his air force to kill civilians after the Libyan leader violently cracked down on pro-democracy protests.
NATO has also conducted air strikes against Kadhafi''s ground forces under the UN mandate to use "all necessary measures" to protect the population.
Following normal procedure, NATO jets were scrambled to intercept the MiG-23 after it was detected by an AWAC surveillance aircraft, the NATO official said.
Two NATO planes flew alongside the MiG and made visual contact with the Libyan pilot, using international signals to indicate that he should land. The signals are usually made by hand or by tipping the plane's wing.
"He complied and the aircraft landed very quickly after take off, the official said. "It was only in the air a few minutes." "In this case there was no aggressive behaviour, which meant no lethal force was required," the official said.
NATO assumes the pilot was part of the opposition because Benghazi is in the hands of rebels who have commandeered several Libyan fighter jets.
"It shows we are impartial, the no-fly zone applies to any aircraft," the official said. "A no-fly zone is a no-fly zone, period." The intercept came in the wake of two friendly fire incidents in Libya.
NATO warplanes mistakenly struck a column of rebel tanks on Thursday, killing four people. The alliance admitted that it was unaware that the rebels were using tanks in the conflict.