The MPs, whose names have not been publicised, were in Prime Minister James Marape's camp during the ongoing political standoff, Radio New Zealand reports.
PNG pandemic response controller David Manning said an MP was initially tested at the weekend and returned a positive result. The MP was then isolated from the rest of the government camp at Loloata Island, Central Province, but that contact tracing unearthed more cases.
"As a result of further tests we did pick up another two positive cases, and of course they have now been isolated as well," Manning told a media conference in Port Moresby.
"I have written in my capacity as controller to the Speaker of the national parliament, advising him of the three positive cases, and as such I have recommended to him, consistent with our procedures as to what we expect in how to respond to this in so far as the parliament is concerned."
Health officials said any recall of parliament would need to follow safety guidelines. In the meantime any other MPs or parliamentary staff who have been in contact with the MP at the Loloata resort are to be isolated and tested.
All three cases are described by health officials as having mild symptoms. The new cases in the National Capital District take PNG's total number of confirmed infections to date to 633.
Local media is also reporting that another MP who had been at the Loloata camp had since also left for Vanimo in PNG's northwest, where opposition MPs are camped.
Health officers in Vanimo have been directed to test the MP and close contacts.