The U.S. 10-year Treasury yield, which moves inversely to the bond's price, moved lower to 1.702 percent, after closing at 1.729 percent on Tuesday. This is down from 2.3 percent at the start of the year, as safe-haven buying has continued to weigh on yields.
The rallied to 0.702 percent, after earlier flattening the 2-year, 10-year yield curve below 100 basis points, the flattest it has been since Dec. 2007. Meanwhile, the longer-dated 30-year yield fell to 2.526 percent after finishing at 2.555 percent in the previous session.
The Treasury Department auctioned $23 billion in 10-year notes at a high yield of 1.73 percent Wednesday.
The bid-to-cover ratio, an indicator of demand, was 2.56.
Indirect bidders, which include major central banks, were awarded 62.3 percent. Direct bidders, which includes domestic money managers, bought 15.3 percent.
Yellen's prepared comments released on Wednesday morning stated that conditions are less supportive of growth and that monetary policy is not on a preset course. She also reiterated that the rate path is data dependent.
All eye were on central bankers' speeches in Washington Wednesday, with the European Central Bank's Peter Praet slated before Yellen.
Yellen is scheduled to testify on the economy before congressional committees Wednesday and Thursday. She is likely to be asked about everything from rate hikes to banking reform. But her bigger audience will be world financial markets, rattled by the fact that the Fed's forecast continues to show rate hikes as markets gyrate over fears of a weakening world outlook and divergent central bank manoeuvring.
She began speaking before the House Committee on Financial Services at 10 a.m. ET Wednesday.
Head of rates strategy at Mizuho International, Peter Chatwell expects price action to remain weak on Wednesday as a lot of uncertainty still remains around what Yellen might say.
"In the case of the Fed because a biased interpretation of last Friday's jobs data could be used to justify continuing on a hiking path. This would be damaging to a weakening US economy. Inversely a too sharp change of course would send a distressing signal to investors that the central bank was wrong to hike rates in December. It would also imply that the economy is in a worse state than it previously admitted," he said.
Other data due for release on Wednesday included the Federal Budget at 2:00 p.m. ET.
— Reuters contributed to this report.