WASHINGTON (AP) — Interest rates on short-term Treasury bills were mixed at Monday's auction with rates on three-month bills rising to the highest level since February while rates on six-month bills were unchanged.

The Treasury Department auctioned $30 billion in three-month bills at a discount rate of 0.100 percent, up from 0.095 percent last week. Another $27 billion in six-month bills was auctioned at a discount rate of 0.150 percent, unchanged from last week.

The three-month rate was the highest since these bills averaged 0.115 percent on Feb. 27.

The discount rates reflect that the bills sell for less than face value. For a $10,000 bill, the three-month price was $9,997.47 while a six-month bill sold for $9,992.42. That would equal an annualized rate of 0.101 percent for the three-month bills and 0.152 percent for the six-month bills.

Separately the Federal Reserve said Monday that the average yield for one-year Treasury bills, a popular index for making changes in adjustable rate mortgages, edged up to 0.21 percent last week from 0.19 percent the previous week.