A human skull has been found on a beach by a man who says he called police and was told to hide it until they could get there.

It was spotted by Darwin man Chris Johnson while he was fishing for crabs on a beach in the Mandorah area, about 130km by road from Darwin, about 3pm (ACST) on Friday.

Mr Johnson posted photos of the skull on his Facebook page.

"Yep!! Called the Po Po (the police)... They want me to hide it!! They are going to come around," he wrote.

Mr Johnson said he had caught several crabs and had packed up his equipment when he made the discovery as he left.

"It's pretty heavy, it's like a bowling ball, it's all full of sand," he told the ABC.

He said after police told him to hide it, he took the skull and placed it in scrubland away from the water.

"The police instructed me to go and hide it in the bush somewhere, so I did that," he said.

Mr Johnson said police asked him to hide the skull. ( Facebook )

Mr Johnson said police told him they would call when they were leaving for the site but "they never did".

"It's a secluded beach, you can't even take a car there... it's pretty boggy sand," he added.

Mr Johnson said he felt uncomfortable at the thought the skull was still where he left it on Friday.

"It's definitely still there. I just feel uneasy that there is a human skull sitting exposed out there in the bush. That's just how I am," he said.

The area is believed to be a traditional Aboriginal burial site.

Northern Territory police said no action was likely to be taken until Monday and refused to confirm whether they had visited the site yet.

Superintendent Robert Burgoyne said the discovery was not being treated as a crime scene, and it must therefore seek permission to enter the site from Aboriginal Areas Protection Authority (AAPA).

But AAPA CEO Ben Scambary told the ABC his organisation no longer handled burial site issues and it was a matter for the Heritage Branch of the NT Government.

Supt Burgoyne said police records did not show Mr Johnson was advised to move the skull.

"Our information is he removed it himself and was not instructed by police," he said.

In 2010, two men fishing for crabs near the Mandorah Hotel found a skull and bones in a sand bank.

That find occurred within a registered sacred site that includes a number of traditional Aboriginal burial grounds in the Mandorah area.