By Corrie Driebusch And Saumya Vaishampayan 

U.S. stocks were little changed Friday ahead of a speech by Federal Reserve Chairwoman Janet Yellen scheduled for this afternoon.

Stock-trading volume was muted Friday ahead of the long weekend, mirroring the past several trading sessions. The week is on pace to be the slowest since the week including New Year's Day. The stock market will be closed Monday for Memorial Day.

The Dow Jones Industrial Average fell 21 points, or 0.1%, to 18265. The S&P 500 slipped a fraction to 2131 while the Nasdaq Composite rose 11 points, or 0.2%, to 5102.

As first-quarter earnings season draws to a close, investor focus is largely back on the timing of any interest-rate increase by the Federal Reserve, traders said. With little else occurring in the market Friday, they said all eyes are on Ms. Yellen, who is scheduled to speak about the U.S. economic outlook at 1 p.m. ET.

"The major story today is Yellen," said Neil Massa, senior equity trader at John Hancock Asset Management. "Volume is light and a lot of trading desks aren't fully staffed, so it will be interesting how the markets take what she says."

With such little liquidity in the market, reaction to Ms. Yellen's comments could result in exaggerated market moves in either direction, he said.

Earlier Friday the Labor Department released a stronger-than-expected reading on inflation in April.

The consumer-price index rose 0.1% in April from a month earlier, the Labor Department said Friday. Excluding the food and energy categories, so-called core prices gained 0.3%, the largest increase since January 2013. Economists surveyed by The Wall Street Journal had expected overall prices to increase 0.1% and core prices to rise 0.2%.

Federal Reserve officials are watching for signs that inflation is picking up as they debate when to raise short-term rates for the first time since June 2006.

Stocks rose Thursday, propelling the S&P 500 to a record close. The S&P added 0.2% to 2130.82. The Dow was up 0.34 point to 18285.74, ending 0.1% below its most recent record of 18312.39.

The Dow industrials have risen 0.1% for the week through Thursday's close. The S&P and Nasdaq are on track to post more substantial gains, up 0.4% and 0.8% in the same period, respectively.

"We've got the Dow and S&P touching new highs, but it doesn't seem to be with very much enthusiasm," said Colin Cieszynski, chief market strategist at CMC Markets.

In Europe, Germany's DAX slipped 0.4%, while France's CAC 40 was flat.

In commodity markets, gold futures added 0.1% to $1205.40 an ounce. Crude-oil futures lost 1.4% to $59.90 a barrel. The yield on the 10-year Treasury note was at 2.209%, compared with 2.186% on Thursday. Yields fall as prices rise.

In corporate news, Deere & Co.'s shares rose 3.7% after the farm equipment producer reported its profit dropped in the latest quarter though results were still better than feared.

Campbell Soup Co. reported its profit easily topped expectations in the latest quarter as the company scaled back promotions and began implementing cost-cutting plans. Shares rose 2.1%.

Aéropostale Inc. shares tumbled 13% after the teen retailer projected a wider-than-expected loss for the July quarter.

Write to Corrie Driebusch at corrie.driebusch@wsj.com and Saumya Vaishampayan at saumya.vaishampayan@wsj.com