The Department of Foreign Affairs (DFAT) has confirmed an Australian man is on trial for alleged terrorism-related offences in Saudi Arabia.

DFAT says the 25-year-old, named in the media as Shayden Thorne from Perth, was arrested 18 months ago and is being detained in a prison outside Riyadh.

His brother, Junaid Muhammed Thorne, 23, is also in the country but is in hiding after being released from prison after two months of detention without being charged.

Junaid's cousin, Stephanie Riley, says Shayden was arrested after police found terrorism-related material on a laptop that he had borrowed.

Their mother, who did not want to be named, told NITV that Shayden has been tortured during his detention.

Both brothers have lived in Saudi Arabia for more than a decade, although they have kept their Australian citizenship.

"I want them to clear his name and I want them to send him home," their mother said.

In hiding: Junaid Thorne, who was detained in Saudi Arabia for protesting his brother's arrest.

"All the evidence they got against him was extracted through torture. They deprived him of sleep; they continually had him under bright lights."

Junaid, who was arrested for protesting his brother's imprisonment, says he is in hiding after having his passport confiscated by Saudi authorities.

"Any checkpoint or any police officer that stops me and asks for my identity card and realises that I am Muhammed Junaid, I'd be arrested straight away," he told Australian Indigenous TV station NITV via Skype.

Safety fears

The men's mother said Junaid "just wants to come home".

"My son contacted me and said he feared for his safety," she said.

"He thought they would arrest him again and he didn't want to go back to prison."

Ms Riley says she is in constant contact with Junaid.

"He was in good spirits knowing that we've gone to the media and he feels confident that something is going to be done very soon," she said.

DFAT has confirmed that consular officials have been assisting Shayden since his arrest in November 2011.

DFAT officials are also assisting the men's family in Australia.

The Greens say Shayden's detention is an "outrageous abuse of his rights".

WA Senator Scott Ludlam says the Government must "vigorously" investigate the claims of torture.

"Saudi Arabia is not renowned for due process, rule of law or fair treatment of suspects," said WA Senator Scott Ludlam.

"It is essential that the Federal Government makes the maximum effort to protect the human rights of Junaid and Shayden Thorne.

"It is essential that Foreign Minister [Bob] Carr does all he can to ensure the fair treatment of these two Australians."