A local woman saw the large animal, which she described as three feet long and dark coloured just yards from her home in Crawton, south of Stonehaven, early on Tuesday morning.
And the creature was just seconds away from attacking her neighbour's domestic cat.
The woman said: "I got up in the morning and heard a very loud noise from outside. It was really quite unusual, like a screech. I thought something must have got an animal. That was when I saw something behind the grass at the fence about 20 feet from my front door. I was shocked."
She continued: "I totally freaked when I saw it and ran up to the fence. It had an animal cornered – I think it was the neighbour's cat – but as soon as it heard me it just took off straight across the field. It was smooth-haired and sleek.
"I ran inside to get my binoculars to try and get a better look at the beast. I looked at it through them and it turned around and looked at me. Then it shot off over the field. It ran so fast it was unbelievable. It was clearly a cat - there was no way that it was a dog or anything like that. "
The Crawton resident immediately alerted her neighbours, some of whom own sheep which are ready to lamb, to warn them of the possible danger.
The big cat is the first to be seen in the Mearns for several years. There were a number of reported sightings of a cat dubbed "The Beast of the Mearns" around Stonehaven in the late 1990s in the Mineralwell area and near Mackie Academy.
The Dangerous Wild Animals Act in 1976 to ensure that anyone keeping an animal such as a big cat would keep it in purpose-built secure accommodation. It is believed many owners who found they could not cope with the cost and commitment of these animals simply released them into the wild, where they may have bred.