The aircraft was en route from Dubai to Oslo with 192 passengers and crew members on board when it carried out a "safety landing" in Shiraz in southwestern Iran because of engine trouble on December 14, a Norwegian Air Shuttle spokesman, Andreas Hjornholm, told AFP.
While passengers were able to fly on to Oslo the following day on another aircraft, the Boeing 737 Max has been stuck on Iranian soil where the airline's mechanics are trying to repair it, Hjornholm said.
According to specialized sites such as www.airlive.net, the repair work has encountered problems because international sanctions bar the airline from sending spare parts to Iran.
With the US withdrawal from the Iran nuclear deal, the Trump administration decided to reimpose sanctions on Tehran.
Norwegian Air Shuttle refused to comment on those reports.
"I can only say that we are working with several options to get the plane back on the wings, and right now we are waiting for our technicians to be able to service the plane and to get it working," Hjornholm said.
It could also pose problems for the plane's passengers and crew members if they want to travel to the US in future.
According to Hjornholm, the passengers and crew on the Dubai-Oslo flight officially entered Iran and stayed overnight at a hotel on December 14-15.
The US Embassy in Oslo was not available for comment.
Last year, former NATO secretary general Javier Solana was refused entry to the US because he had visited Iran for the inauguration ceremony of President Hassan Rouhani in 2013.