The company constructed the power plant and started operations in 2010.
DONG will sell the equity in the company for an aggregate price of NOK1.8bn ($287m).
The company is selling the power plant as part of its financial plan to sell its non-core assets. DONG has announced its intention to divest non-core activities at a value of NOK10.7bn ($1.7bn) in 2013-2014.
DONG Energy CEO Henrik Poulsen said, "With the divestment of Mongstad, we are taking another significant step towards the realisation of our financial action plan."
The deal is expected to close in the third quarter.
The company has so far divested nearly NOK9.6bn ($1.53bn) of non-core assets.
