Interest rates on short-term Treasury bills were mixed in Monday’s auction. Rates on three-month bills were unchanged, and rates on six-month bills fell to the lowest level since mid-September.

The Treasury Department auctioned $32 billion in three-month bills at a discount rate of 0.09 percent, unchanged from last week. Another $28 billion in six-month bills was auctioned at a discount rate of 0.135 percent, down from 0.14 percent last week. The six-month rate was the lowest since these bills averaged 0.13 percent on Sept. 17.