The woman was not injured but was left shaken.
The youth is described as being approximately 15 years old, of heavy build, approximately 5’2” tall, with dirty fair hair and a pale complexion.
He was wearing a red zipped hooded top, black school trousers and black leather pointed shoes.
It is believed that he made off in the direction of Twinbrook.
Anyone with any information about this incident or who has noticed any suspicious activity in the area is asked to contact Lisburn Police Station on 0845 600 8000. Or if someone would prefer to provide information without giving their details, they can contact the independent charity Crimestoppers and speak to them anonymously on 0800 555 111.