It happened Saturday on Highway 71 South outside Fort Smith in the Rye Hill area.
Deputies were called to the scene after getting calls about a man who was stepping into traffic. When deputies arrived they found the victim who was described as "visibly shaken."
The man told them the woman who took his truck had been walking down the road and flagged him down. When he pulled over, she pointed a pistol at him, deputies said.
The woman was described as a "small blonde-haired lady" with a "very skinny face" and waist-length hair, who was wearing dark jeans and a black leather jacket.
The man said he was ordered to get out of the truck and walk away, which he did. When the man crossed over the lanes of traffic and went into the median, the woman drove away.
The man told deputies he went back across the road and found his wallet lying on the shoulder of the highway. He said his $300 in cash was missing. The man's cellphone was also found near the highway by deputies.
The missing vehicle is a red 2006 Dodge Ram 2500 with an Oklahoma license plate.
Anyone with information is asked to contact the Sebastian County Sheriff's Office at (479) 783-1051.