The man fled before police arrived, and the woman said she feared the popular beach was not safe for children while he remained at large.
A police spokeswoman confirmed officers were deployed to the area after the man was reported ''masturbating in public'' near Victoria Rd.
Several officers swooped on the area, scouring the sports ground and dunes near the beach, but the man had apparently fled the scene.
The woman, who did not want to be named, said that her daughter had seen the same man acting inappropriately on the beach a few weeks ago.
She commended officers for their attentiveness regarding her daughter and thorough work after that incident.
But she remained worried the man would continue to perform indecent acts in the area.
''I'm very concerned about children coming to this beach.''
She described the man as being in his early 30s, about 1.68m tall with black hair.
There have been a series of reports of men performing lewd acts in the area of St Kilda and St Clair Beaches this year, as well as at the Dunedin Botanic Garden.
Late last month, police converged on St Clair seeking a naked man who was exposing himself in the sand dunes, but were unable to apprehend him.
• Dunedin police (03) 471-4800, Crimestoppers 0800 555-111.
