A police operation targeting sex offences on public transport has charged a man over an incident near Bargo.
Police allege the 41-year-old man got on a train at Bargo station at noon on August 6.
He sat next to a 16-year-old girl and allegedly exposed his genitals and began committing a sexual act.
When another person entered the carriage, he stopped.
The teenage girl got off the train and reported the incident to police.
As part of Operation Artemis, Campbelltown Police Transport Command officers investigated.
On Tuesday they arrested the man at Silverwater jail and charged him over the incident.
He is due to appear in Campbelltown Local Court on Wednesday.