The state's Security Investigation Group is investigating the discovery of a small improvised explosive device in Minninup Beach car park on Tuesday, October 22.
The device was located by a member of the public and seized by WA Police Force, with a forensic examination of the device later confirming that it could have been detonated.
A WA Police Force spokesperson said the find was concerning and that the person responsible for leaving it there appeared to have no regard for the safety of others.
"Fortunately no one was injured, however it is simply unacceptable that someone is willing to expose other community members to such danger," the spokesperson said.
Despite an extensive search of the area, no other items were located and police confirmed they were still trying to determine how long the device had been there and whether it was intentionally left there.
The Investigation Group called on those who may have information regarding the device, or who saw suspicious activity in the vicinity of the Minninup Beach car park on or before October 22 to come forward.
Anyone with information is asked to contact Crime Stoppers on 1800 333 000 or report the information online at www.crimestopperswa.com.au
The find comes just five years after a Bunbury man was sentenced to two-and-a-half years jail over making bombs and planting them in the Leschenault Estuary.