U.S. stocks open higher ahead of Yellen's speech

U.S. stocks opened mildly higher Monday as investors awaited a speech from Federal Reserve Chair Janet Yellen in the afternoon.

Yellen will speak on the job market at a University of Baltimore commencement. This is the last of the Fed's speeches before the Christmas break and will be followed for any additional guidance on monetary policy.

Last week, the U.S. central bank decided to raise the target range for the federal funds rate to 1/2 to 3/4 percent.

The Fed also released its updated economic projections, which indicated that the central bank forecasts three rate hikes next year, while in its September projections, Fed officials expected only two rate hikes in 2017.

On the economic front, the Markit services purchasing managers index for December is scheduled for release later in the morning.

Shortly after the opening bell, the Dow Jones Industrial Average rose 10.53 points, or 0.05 percent, to 19,853.94. The S&P 500 edged down 1.39 points, or 0.06 percent, to 2,259.46. The Nasdaq Composite Index decreased 3.14 points, or 0.06 percent, to 5,440.30.

U.S. stocks reversed early gains to end lower Friday. Endi