The Nationwide building society index is based on the price agreed, after a survey, by its mortgage customers.
It found that prices fell by 5.7% in the second quarter of 2010, compared to a 1% fall in the first quarter.
Northern Ireland was the only UK region to see a fall in prices in the second quarter.
On an annual basis, prices were down 5.2% - a slight deterioration from the 3% year-on-year fall in the first quarter.
Nationwide's chief economist Martin Gahbauer noted that unemployment has continued to rise in Northern Ireland and is the joint highest across the building society's house price regions.
The survey suggests the average price of a house in Northern Ireland is now £128,846.
It also suggests average prices for four regions within Northern Ireland:
City of Belfast - £191,536
Northern Ireland (North East) - £145,905
Northern Ireland (South East) - £160,423
Northern Ireland (West) - £114,592
The finding are broadly in line with other recent house price surveys.
Northern Ireland experienced a house price bubble in the first half of this decade but since about 2007 prices have plunged.
BBC
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