A screen grab of the moment was tweeted by CNBC staffer Steve Kopack, and later shared by others who have been watching Yellen's testimony before Congress. The buck is rising against the Euro, but is down against both the British pound and the Japanese Yen.
The dollar has climbed to around $1.1420 against the Euro Wednesday afternoon, from an early low of $1.1489. The U.S. Treasury budget data for June will be released at 2:00 p.m. ET.
Sterling rose for a send straight day against the greenback and was up 0.38 percent to $1.2931. (NYSE: HD), Microsoft Corp (NASDAQ: MSFT) and McDonald's Corp (NYSE: MCD) each rose at least 1.1%.
The kiwi and Aussie dollars rode out a poor set of New Zealand data to stand 0.6 per cent higher on the day, leading gains for the G10 group of developed world currencies along with the Swedish crown.
Looking ahead, Canada new housing price index for May, US PPI for June and US weekly jobless claims for the week ended July 8 are slated for release In the NY session.
Futures on the S&P 500 Index were little changed.
Also, the unemployment rate dropped to a pre-recessions level of 4.4 percent in June, from a high of 10 percent in 2010. If inflation continues to undershoot the Fed's 2% target-so-called "core" inflation has drifted downward every month this year, from 2.3% in January to 1.7% in May-then more traders may revise their expectations for Fed actions in the future.
The figure was the lowest since 1975. Final demand prices were unchanged in May and rose 0.5% in April.
Oil prices wavered early Wednesday, but recovered after a report showing that USA crude-oil inventories declined sharply last week.
About four stocks advanced for every decliner on the New York Stock Exchange, with an exchange volume of 458.30 million and a composite volume of 2.205 billion in afternoon trade.
The estimate offset solid import data from China, the world's biggest energy consumer, which showed crude imports for the month of June rose 19% from a year ago to 8.79 million barrels per day. "Yellen still expects the balance sheet normalisation process to begin this year but this is anticipated to be a very slow process", Mr O'Loughlin added.