NEW YORK (CNNMoney.com) -- Mortgage rates headed back up after many weeks of declines, according to a survey released Thursday.

The 30-year fixed-rate mortgage (FRM) averaged 6.37 percent for the week ending Oct. 12, up from 6.30 percent, according to Freddie Mac's (Charts) Primary Mortgage Market Survey. A year ago, the 30-year FRM averaged 6.03 percent.

The 15-year FRM averaged 6.06 percent this week, up from 5.98 percent last week. A year ago, it averaged 5.62 percent.

Rates for five-year adjustable-rate mortgages (ARMs) came in at 6.10 percent this week, up from 6.00 percent last week. A year ago, they averaged 5.57 percent.

One-year ARMs averaged 5.56 percent, up from 5.46 percent last week. A year ago, the one-year ARM averaged 4.85 percent.

"Renewed concern that inflation is still an issue put some upward pressure on bond yields, which generally translates into higher interest and mortgage rates," Frank Nothaft, Freddie Mac's chief economist, said in a statement.

"ARM rates especially felt the weight of increased inflation fears, narrowing the gap between ARMs and fixed-rate mortgage rates. Thus, ARMs may become less desirable."

Freddie Mac competes on the secondary market with Citigroup (Charts), Countrywide Financial (Charts) and Fannie Mae (Charts).

Realtors: Home sales weaker, prices lower Trade group expects 1.6 percent rise in median prices, a smaller increase than forecast last month.

Beware the mortgage time-bomb That ridiculously low-rate ARM seemed like such a good idea at the time. But now, payments will be coming due in a big, big way.