Interest rates on short-term Treasury bills declined in Monday's auction with rates on six-month bills falling to the lowest level in five weeks.

The Treasury Department auctioned $35 billion in three-month bills at a discount rate of 0.095 percent, down from 0.110 percent last week. Another $30 billion in six-month bills was auctioned at a discount rate of 0.115 percent, down from 0.120 percent last week.

The three-month rate was the lowest since three-month bills averaged 0.085 percent on Feb. 11. The six-month rate was the lowest since those bills averaged 0.110 percent on Feb. 4.

The discount rates reflect that the bills sell for less than face value. For a $10,000 bill, the three-month price was $9.997.59 while a six-month bill sold for $9,994.18. That would equal an annualized rate of 0.096 percent for the three-month bills and 0.117 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, declined to 0.15 percent from 0.17 percent last week.