Andrew Shinnie opened the scoring for the hosts nine minutes into the second half, and McKay wrapped up victory with goals in the 61st and 78th minutes.
Caley Thistle keeper Antonio Reguero was called into action early, tipping over an effort from Aberdeen's top scorer Niall McGinn.
At the opposite end Richie Foran tested keeper Jamie Langfield, who turned the chance wide.
Jonny Hayes had another chance at the mid-point of the first half but Reguero was equal to his low shot.
Just before half-time, Joe Shaughnessy curled an attempt wide as neither side could be separated at the break.
Aberdeen started brightly with Hayes cutting inside Graeme Shinnie and Gary Warren before being thwarted by a terrific save from Reguero.
It proved crucial as Inverness made the breakthrough through Andrew Shinnie on 54 minutes.
After being played in by Aaron Doran, he cut inside Dons captain Russell Anderson then rifled the ball past Langfield into the roof of the net from an acute angle. It was the Scotland attacking midfielder's 12th goal of the season.
Seven minutes later Mckay doubled Inverness's lead. The SPL's top scorer showed composure to tuck the ball past Langfield from 10 yards after being found by Ross Draper.
Midfielder Draper could have made it three when he beat the offside trap after a Foran through ball and guided the ball inches wide.
Another goal did arrive seconds later when McKay thundered a shot from the edge of the area home in 78 minutes. Raven's cross was flicked on by Andrew Shinnie and the Northern Ireland international netted for his 20th of the season.
Aberdeen showed little resistance as the hosts saw out the closing stages comfortably.