The woman, who was also there with her husband, said the man was there for about 30 minutes before she realised what he was doing and called the police.
She said she wanted to let others know - particularly mothers with children who visited the playground regularly - in a bid to raise awareness.
A police spokesman confirmed to the Herald that officers were called to the scene about the incident.
"Police received one report of a man sitting on a park bench on Point Chevalier Road at 11.48am, Saturday, with his hands down his pants.
"Police attended and the man left shortly after midday.''
The spokesman said there was no record of the man involved being arrested.
