Stock futures on all three major U.S. stock markets traded in positive territory, with Dow Jones industrial average futures up over 80 points in early London trade.
Read MoreIt's the central bankers vs. earnings
Investors have a slew of earnings to digest. Goldman Sachs,Citigroup, Blackstone, Charles Schwab, UnitedHealth, eBay and Phillip Morris are among the firms reporting second-quarter earnings before the market open.
Google, Schlumberger, Mattel, Advanced Micro, Celanese and Cintas are expected to report after the closing bell.
U.S. jobless claims data are due out at 08:30 a.m. ET, following by the Philadelphia Fed survey and NAHB homebuilders' survey at 10 a.m.
In addition to the earnings and data, markets await Yellen's testimony to the Senate Banking Committee. On Wednesday, Yellen reiterated recent comments that interest rates are likely to rise this year.
"These tend to go largely the same way as yesterday's event but should still be monitored closely for any surprises, of which there were none yesterday," Craig Erlam, senior market analyst at currency trading firm Oanda, said in a note.