The group, the Detroit-based Earth Liberation Front, is linked to a spate of arson attacks near Ford's country home. The Ford chief executive is thought to have become a target because he is building a family home on a secluded $600,000 plus plot of land.
The FBI and state police warned Mr Ford to step up security and to keep public appearances to a minimum. The warnings came as the car company celebrated its centennial last weekend. It was feared the Earth Liberation Front, a shadowy group with a large presence in the Detroit area, would strike during the event.
The ELF has stepped up its attacks against property and cars over the past two months. It has claimed responsibility for arson attacks against luxury homes under construction.
At least five houses have been burnt down in areas near Mr Ford's family home in the past two months.