The official warning was given to the batsman after the home team's nine-wicket defeat to Bangalore at the Wankhede stadium.
Sharma admitted to have breached Level 1 offence (Article 2.1.2) of kicking the stumps at the end of the match.
For Level 1 breaches of the IPL code of conduct, the match referee's decision is final and binding.
Mumbai have 14 points after 12 games and are placed third in the table.
