U.S. fixed mortgage rates this week remained at all-time record lows, which served as an incentive for refinancing and purchasing, said the Primary Mortgage Market Survey released on Thursday by Freddie Mac.

The mortgage giant said that 30-year fixed-rate mortgage (FRM) was 3.87 percent for the week ending Feb. 9, matching last week's figure. Last year at this time, the 30-year FRM averaged 5.05 percent.

The 15-year FRM averaged 3.16 percent, up from its previous week average of 3.14 percent. A year ago at this time, the 15-year FRM averaged 4.29 percent.

The 5-year Treasury-indexed hybrid adjustable-rate mortgage ( ARM) averaged 2.83 percent, up from last week when it averaged 2. 80 percent, but the 1-year Treasury-indexed ARM averaged 2.78 percent this week, up from last week's 2.76 percent.

The average rates don't include extra fees, known as points, which added the rates up by 0.6 percent to 0.8 percent.

Mortgage rates remained below 4 percent because they followed the yield on the 10-year U.S. Treasury note, which was around 2 percent.

To calculate average mortgage rates, Freddie Mac collects rates from lenders across the country on Monday through Wednesday of each week.

Freddie Mac was established by the Congress in 1970 to provide liquidity, stability and affordability to the nation's residential mortgage markets.