Traders were waiting to hear whether Yellen will reinforce the notion the central bank will consider raising rates at its Dec. 12-13 policy meeting even as inflation remains below its 2-percent goal, analysts said.
"It seems unlikely that Chair Yellen's tone and core views will have changed dramatically from Wednesday's FOMC press conference," NatWest strategists wrote in a research note.
Investors were also preparing for the upcoming supply of two-year Treasuries at 1 p.m. (1700 GMT).
Yellen is scheduled to speak at 12:45 p.m. (1645 GMT) about "Inflation, Uncertainty, and Monetary Policy" at the National Association for Business Economics' annual conference in Cleveland.
Last Wednesday, the policy making Federal Open Market Committee left the door open for another rate increase in December and said it will begin to reduce its $4.5 trillion balance sheet in October.
The rise in US yields was stoked further by remarks from US President Donald Trump who said and lawmakers were working to pass a big tax cut for the middle class. Traders had no details on the plan, but speculated it might raise the federal deficit and increase government borrowing.
"It should be positive for risky assets and negative for Treasuries," said Larry Milstein, head of government and agency trading at R.W. Pressprich & Co. in New York. "Frankly, there is a lot of skepticism until we see the details."
At 11:49 a.m. (1549 GMT), the yield on benchmark 10-year Treasury notes was up nearly 2 basis points at 2.237 percent, while the 30-year bond yield increased over 2 basis points to 2.782 percent.
Bond yields declined on Monday on safe-haven demand due to tensions between North Korea and the United States and surging support for the far right in Sunday's German election.
Several other Fed officials are set to speak publicly, including Fed Governor Lael Brainard, Cleveland Fed President Loretta Mester and Atlanta Fed President Raphael Bostic.
In "when-issue" activity, traders expected the two-year note issue to sell at a yield of 1.458 percent, which would be highest yield since October 2008.