WASHINGTON (AP) — U.S. long-term mortgage rates rose this week amid optimism over prospects for the U.S. economy. Rates remain at historically low levels, however, as an incentive to prospective homebuyers.

Mortgage giant Freddie Mac says the average rate for a 30-year fixed-rate mortgage jumped to 3.75% from 3.69% last week. By contrast, the benchmark rate stood at 4.94% a year ago.

The average rate on a 15-year mortgage increased to 3.2% this week from 3.13% last week.

Federal Reserve Chairman Jerome Powell told Congress this week that the central bank remains optimistic about the U.S. economy, though it still faces risks from slower growth overseas and trade tensions.