Miles Bridges' baby mama, Mychelle Johnson, is accused of assault and battery on the NBA star ... TMZ has learned.

According to new legal docs, obtained by TMZ, Mychelle is facing a misdemeanor charge in North Carolina for allegedly throwing water on Miles during a custody exchange ... dousing him in full view of their children.

In the docs, Miles claimed that during a June 22 custody exchange, Mychelle "threw water on me in front of the kids and said she'll do it again if we argued."

Miles said he asked her why she did it … and she told him it was because they were arguing. As a result, he says he's "scared for my kid's safety."

The criminal charge comes as Miles and Mychelle continue to go back and forth over custody of their kids.

Miles was granted a temporary restraining order against Mychelle earlier this year … after claiming she was cyberstalking him and showed up to one of his games in an attempt to mess with his car. Mychelle denied the claims.