Yellen, who spoke after the market closed, may have slightly recalibrated expectations for a rate rise, by saying she personally anticipates a hike this year.
Traders had hoped the speech would clarify the central bank's position on rate hikes, after last week's FOMC meeting and a week of volatile markets.
The Fed chair said it would likely be appropriate to raise rates from near zero "sometime later this year," though the decision would continue to rely on economic data. In her comments last week, she had not identified herself as part of the group favoring rate hikes this year, but she had made a similar comment during the summer.
Dow futures traded about 210 points higher after briefly gaining 250 points, while S&P 500 and Nasdaq futures also indicated a higher open.