The King and Queen, who are both 83, are said to be feeling well and have not reported any COVID-19 symptoms. An official said the royal couple are to take COVID tests themselves and further announcements will be made when the results are available.
The officials said 14 employees at the Royal Court in Oslo are also self-isolating.
King Harald tested negative for coronavirus last month ahead of a heart valve replacement operation which took place after he suffered breathing difficulties.
King Harald and Queen Sonja are expected to continue their work from isolation as much as is possible.
Crown Prince Haakon Magnus, 47, will take over his father’s role with the President of Estonia at a planned event on 20 November.
The royal couple went into quarantine back in March after a state visit to Jordan.
At the time King Harald said: “Our country is in a serious situation that affects individuals and society as a whole.
“It is crucial that we all participate in the national quest to avoid exposing ourselves or others to infection.
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“It is therefore important that we all follow recommendations and orders from the authorities.
“We must contribute what we can to prevent the spread of the virus, and I would especially like to thank health professionals all over the country who are doing their utmost to remedy the situation these days.
“We all hope that developments will soon turn around.”
Norway has reported 31,722 cases of coronavirus since the pandemic began in early March and a total of 305 deaths.
People travelling to the country from most other European nations must provide a negative result taken no more than 72 hours before their arrival.