The 9967sq m site consists of 12 lots and at September 2015 had an estimated value of $5.5 million.
NRC spokesman Phil Heatley said yesterday the building had still not gone unconditional yet because the potential buyers were doing their due diligence.
He could not divulge the potential buyer's identity or other details, including the price.
The site was originally bought as a commercial investment and had not been inherited from the former Northland Harbour Board, as had other NRC properties.
Last year the NRC turned down a proposal from Whangarei disability support group NorthAble to buy the property and turn it into a healthcare hub.