He stopped his car to investigate but says the trio ran away "faster than any man he had ever seen".
The police officer said he heard the "the sound of static electricity" as he approached the figures who were all over 6ft tall with blond hair.
The officer returned to his home in Marlborough, Wiltshire, and contacted paranormal experts and told them he had spotted a UFO.
Crop circle researcher Andrew Russell, who is investigating the sighting on behalf of the officer, revealed how he described the close encounter.
"He shouted to the figures who, at first, ignored him, not glancing at him. When he tried to enter the field they looked up and began running," he said.
"He said: "They ran faster than any man I have ever seen. I'm no slouch but they were moving so fast. I looked away for a second and when I looked back they were gone.
"I then got scared. The noise was still around but I got an uneasy feeling and headed for the car. For the rest of the day I had a pounding headache I couldn't shift"."
Wiltshire Police has refused to comment on the incident, which happened in July, saying it is a "personal matter" for the officer involved.