Police are searching for a second man after a bomb was found at a home in Werrington in Sydney's west.

A 23-year-old man was arrested at a Beaumont Hills house on Wednesday after his mother allegedly found a suspicious package in her son's bedroom at her house in Werrington on Tuesday night.

The bomb squad and forensic specialists evacuated the home and removed the homemade explosive where it was later detonated at a local soccer field.

The woman's daughter, Shayleen Butt, said her 22-year-old brother, Harley Turnbull, brought the device home with a friend, not knowing what it was, then both men left.

Her boyfriend, Neil Jones, said the device looked like it could be dangerous.

"[It was] just a little black package about the size of a mobile phone that was taped up with wiring hanging out of it," he said.

"I just wanted to go to sleep, I was tired. It was a big waiting game."

The woman became suspicious and called police.

Inspector Michael Cruickshank said the device had the potential to be catastrophic.

"I believe it was quite small, cylindrical in shape, probably about 15 centimetres long," he said.

"Potentially could be quite catastrophic being an explosive device. Obviously they're dangerous and in the wrong hands.

"I'd also like to stress to the community that this is being investigated as a one-off incident, there were no threats made and no person was put at risk by this incident."

Police said Harley Turnbull, who was arrested at a house on Spur Street in Beaumont Hills, was assisting with police inquiries.