Officers allege the accused (26) threatened the man with a large knife about 9.30pm on April 14.
He allegedly chased the man while carrying the weapon when he attempted to run to his car.
He is accused of stealing the vehicle when the man threw the keys. Police charged him with armed robbery and vehicle theft last Thursday.
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READ NOWHe is due to appear in Joondalup Magistrates Court on July 10.