The plea is expected to be entered by Mars's lawyers on his behalf Wednesday, the Las Vegas Sun reported.
In exchange for the guilty plea, the 25-year-old singer-songwriter will be ordered to spend a year on probation, pay a $2,000 fine, perform 200 hours of community service and complete drug counseling, the newspaper said.
The drug charge stems from Mars's arrest at the Hard Rock Hotel Sept. 19.
He won two Grammy Awards Sunday in Los Angeles.
2014: The Year in Music [PHOTOS]