Mars, whose real name is Peter Hernandez, was in town for a performance at the Hard Rock Hotel. He was taken into custody at 2:40 a.m. after being confronted in the bathroom by police, who discovered the drugs. According to The Associated Press, police said Mars was found with 2.6 grams of cocaine.
He was released without bail early Sunday morning, police told the AP.
The "Just the Way You Are" singer posted a tweet to fans requesting they come out for his gig just hours before the arrest.
"Come See Me @ the Hard Rock 2nite!! VEGAS!!" he wrote on his Twitter account.
Mars has garnered fame this year both for his own album and for his songwriting abilities, as he's penned hit songs for B.o.B. and Flo Rida. He's set to perform with Maroon 5, One Republic and Travie McCoy on several upcoming dates.