However, the price tag of the plan is in the area of $1.5 trillion at a time when the Congressional Budget Official already is projecting a deficit of more than $1 trillion in the years ahead and with the total debt level at $20.6 trillion and rising. Of that total, $14.9 trillion is owed by the public.
The Trump administration contends that the lower tax rates would pay for themselves through growth. In her semiannual testimony before Congress, Yellen was asked about a proposal that would trigger tax hikes if economic goals are not met.
The central bank chief did not specifically comment on the trigger plan but said Congress is right to be thinking about the future of the national debt.
"I would simply say that I am very worried about the sustainability of the U.S. debt trajectory," Yellen said. "Our current debt-to-GDP ratio of about 75 percent is not frightening but it's also not low."
"It's the type of thing that should keep people awake at night," she added.
The Fed has critics of its own, though, who say that the central bank helped balloon the debt through low interest rates kept in place since the financial crisis. The Fed kept its benchmark rate anchored near-zero for seven years, from December 2008 through December 2015. During that time, the national debt grew 77 percent.
Under Yellen, the Fed has hiked rates four times and begun to slowly shrink its $4.5 trillion balance sheet.
During her testimony, Yellen told Congress that she would like the Fed to continue raise rates in a gradual manner until it reaches a point where it feels rates are "neutral," or neither stimulative nor restrictive to growth.