Interest rates on short-term Treasury bills fell in Monday's auction, with the rate on three-month bills dropping to the lowest level since January.

The Treasury Department auctioned $31 billion in three-month bills at a discount rate of 0.076 percent, down from 0.085 percent last week. Another $29 billion in six-month bills was auctioned at a discount rate of 0.140 percent, down from 0.150 percent last week. The three-month rate was the lowest since these bills averaged 0.050 percent on January 30. The six-month rate was the lowest since they averaged 0.130 percent on March 5.

The discount rates reflect that the bills sell for less than face value. For a $10,000 bill, the three-month price was $9,998.10 while a six-month bill sold for $9,992.92. That would equal an annualized rate of 0.076 percent for the three-month bills and 0.142 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, dropped to 0.18 percent last week from 0.20 percent, the previous week.