Treasury bill rates mixed at weekly auction WASHINGTON (AP) — Interest rates on short-term Treasury bills were mixed in Monday's auction with rates on three-month bills rising to the highest level in two weeks and rates on six-month bills falling to the lowest level in six weeks. 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, was unchanged at 0.20 percent last week, the same as the previous week.