Average long-term mortgage rates have fallen for the first time in four weeks and remain near historic lows reached in May 2013.

Mortgage giant Freddie Mac said Thursday that the national average for a 30-year, fixed-rate mortgage fell to 3.75 percent from 3.80 percent last week.

The rate for a 15-year mortgage, popular with homeowners who refinance, fell to 3.03 percent from 3.07 percent last week.

A year ago, the average 30-year mortgage stood at 4.28 percent and the 15-year mortgage at 3.32 percent. Mortgage rates have remained low even though the Federal Reserve in October ended its monthly bond purchases, which were meant to hold down long-term rates.

Economic weakness around the world has lured global investors to the relatively strong U.S. economy. They've bought Treasurys and pushed the yield on the benchmark 10-year Treasury note down to 2.11 percent from 2.79 percent a year ago.

The Fed continues to keep short-term rates near zero. Fed Chair Janet Yellen delivered the central bank's semiannual economic report to Congress last week and indicated that the Fed is still willing to be "patient" before raising short-term rates. The Fed is worried about weak wage growth and inflation well below its 2 percent target.

To calculate average mortgage rates, Freddie Mac surveys lenders across the country at the beginning of each week. The average doesn't include extra fees, known as points, which most borrowers must pay to get the lowest rates. One point equals 1 percent of the loan amount.

The average fee for a 30-year mortgage was 0.6 point, unchanged from last week. The fee for a 15-year mortgage also remained at 0.6 point.

The average rate on a five-year adjustable-rate mortgage fell to 2.96 from 2.99 percent. The fee was stable at 0.5 point.

For a one-year ARM, the average rate was unchanged at 2.44 percent. The fee remained at 0.4 point.