Up to AU$40,000 (NZ$43,000) in cash was found on the Mitchell Freeway in the city's northern suburbs on Monday night, West Australian police said.
"It's like the cash cow had come out and there was cash flying everywhere," Commissioner Col Blanch told Perth radio 6PR on Tuesday.
Members of the public spotted the cash and alerted authorities.
Police arrested a man at the scene and seized cash and an amount of cocaine.
"There was a suspicious meeting on the side of the freeway ... and the fact that we've found cash and the fact that we've found drugs would lead most reasonable human beings to suspect there some type of transaction going on on the side of the freeway," Mr Blanch said.
"I would call it a farcical debacle."
A 34-year-old man was charged with possession of prohibited drugs with intent to sell or supply, possession of stolen or unlawfully obtained property and driving without a licence.
He is due to appear in Joondalup Magistrates Court on Tuesday.
Detectives are searching for a tow truck and motorcycle seen leaving the area when police arrived.