A senator has chased a man through the bush in the Northern Territory after an alleged attempted sexual assault.

Police say a 21-year-old woman was walking along a bicycle path in Katherine, 300 kilometres south of Darwin, when a man grabbed her from behind and dragged her into bushes early yesterday evening.

The woman, who was wearing headphones at the time, fought him off and flagged down a passing car that was being driven by an off-duty policewoman.

A taxi carrying three senators - Nigel Scullion from the Northern Territory, Claire Moore from Queensland and Judith Adams from Western Australia - also saw the woman and pulled over.

"Senator Scullion [chased] the alleged offender for some time before losing him in dense scrub," police said in a statement.

"Senator Moore of Queensland and Senator Adams of Western Australia also stopped to render assistance."

After police launched a public appeal, a 23-year-old man was arrested this morning.

He is currently in custody and will be interviewed by police shortly.

Police Commander Jeanette Kerr praised the Country Liberal senator's efforts.

"This was a quick response provided by one of our off-duty police members, coupled with the actions of Senator Scullion in an attempt to apprehend the offender."