 "Wall Street opens higher as focus shifts to Fed")
Yellen had hinted at higher chances of a rate hike than the markets had priced in, but weak May jobs data and economic repercussions of a possible Brexit forced her to take a dovish stance last week.
CME Group's FedWatch tool see a less than 40% chance of an interest rate increase until December, but will focus on the course of future hikes.
In March, policymakers dialed back the number of rate hikes this year to two from four, citing weak global growth and financial market volatility.
The Fed raised its key overnight lending rate in December for the first time in nearly a decade.
"At this point all eyes are on the Fed. The markets have been over-sold in the short-term and this would be a good place for them to rise, but the key is, will the markets be able to hold on to their gains after the Fed meeting and the conference," said Adam Sarhan, chief executive at Sarhan Capital, adding, "If the markets can't bounce then that's an indication of how weak they actually are."
At 9:38 a.m. ET, the Dow Jones Industrial Average was up 35.58 points, or 0.2%, at 17,710.4.
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The S&P 500 was up 4.45 points, or 0.21%, at 2,079.77.
The Nasdaq Composite was up 8.91 points, or 0.18%, at 4,852.47.
Eight of the 10 major S&P sectors were higher, led by a 0.34% rise in materials. Freeport, which struck a funding deal for a copper project, rose 6.2% to $10.8 and gave the biggest boost to the sector.
May producer price index rose by a better than expected 0.4%, compared with the 0.3% rise analysts had expected.
Whole Foods fell 3.7% after the US Food and Drug Administration warned the grocer over unsanitary conditions in its kitchens.
Advancing issues outnumbered decliners on the NYSE by 1,751 to 895. On the Nasdaq, 1,337 issues rose and 908 fell.
The S&P 500 index showed eight new 52-week highs and no new lows, while the Nasdaq recorded 12 new highs and 12 new lows.