Energy stocks fell along with the price of crude oil.
The Dow Jones industrial average fell 8.01 points, or 0.05%, to 17,492.93.
The Standard & Poor's 500 index fell 4.28 points, or 0.2%, to 2,048.04 and the Nasdaq composite lost 3.78 points, or 0.1%, to 4,765.78.
Investors had little news to interpret and no major economic data to analyse on Monday, so stocks traded in a very narrow range throughout the day.
Roughly three billion shares traded hands on the New York Stock Exchange, making it one of the slowest trading days so far this year.
Several members of the Federal Reserve will be making speeches this week, which may give insight to investors on what Fed policymakers might do at their meeting in June.
Minutes from the Fed's late April meeting showed that policymakers at the nation's central bank seem to believe the US economy has improved enough to warrant higher interest rates.
"Very quiet today," Ryan Larson, head of US equity trading at RBC Global Asset Management, wrote.
"The hesitation seems to directly related to what the Fed may or may not do come its June meeting."
Securities that bet on which way the Fed will move interest rates now show that investors believe there is a 26% chance that interest rates will climb.
In company news, Monsanto rose 4.48 US dollars, or 4%, to 106 US dollars after German company Bayer offered to buy the agricultural products company for 62 billion US dollars.
The deal would make the combined company the world's largest producer of fertilizers and other agricultural products.
Tribune Publishing fell 2.14 US dollars, or 15%, to 12.09 US dollars after the newspaper company rejected a new takeover offer from Gannett.
The company also announced a new investor, who bought a 70 million US dollars stake in Tribune.
Benchmark US crude shed 33 cents to 48.08 US dollars per barrel on the New York Mercantile Exchange. Brent crude, used to price international oils, fell 37 cents to 48.35 US dollars a barrel in London. Energy stocks followed oil prices lower.
In other energy commodities, wholesale petrol rose one cent to 1.65 US dollars a gallon, heating oil fell one cent to 1.48 US dollars a gallon and natural gas fell one cent to 2.06 US dollars per thousand cubic feet.
US government bond prices rose slightly. The yield on the 10-year Treasury note fell to 1.83% from 1.84%. The dollar fell to 109.19 yen from 110.23 yen and the euro fell to 1.1221 from 1.1219 US dollars.
Precious and industrial metals futures closed mostly lower. Gold lost 1.40 to 1,251.50 US dollars an ounce, silver fell 11 cents to 16.42 US dollars an ounce and copper was little changed at 2.06 US dollars a pound.