Speaking at the annual gathering of central bankers in Jackson Hole, Wyoming on Friday, Yellen said the case for a U.S. interest rate rise has strengthened in recent months because of improvements in the labour market and expectations of solid economic growth.
She did not indicate when the U.S. central bank might raise rates, and euro zone bond yields closed lower on Friday.
However, a sell-off in U.S. Treasuries as investors interpreted the comments as hawkish weighed on sentiment in European markets early on Monday.
The German Bund future was down 75 ticks at 166.94.
The 10-year Bund yield rose more than 6 basis points to minus 0.025 percent, the highest level since June 24 when the result of Britain's EU referendum sent shockwaves through markets.