The king shook hands and spoke with people in the crowd near the Church of Christ the Cornerstone, a video taken by Heart News East showed. Chants of "God save the king" could also be heard.
The near two dozen reported protesters were from a group called Republic, which plans to also protest at his coronation in May, according to People magazine.
KING CHARLES ALLEGEDLY HAS EGG HURLED TOWARD HIM, SUSPECT ARRESTED
In a video obtained by the outlet, Charles can be seen walking past individuals holding "Not my king" signs.
Protesters from an anti-monarchy group called Republic held up signs that said "Not my king" during King Charles III's visit to Milton Keynes Thursday. (Samir Hussein/WireImage)
Charles had eggs thrown at him on two separate occasions when he was with Camilla, the queen consort, in November in York, and in Luton, about 30 miles north of London, in December.
King Charles III leaves the Church of Christ the Cornerstone in Milton Keynes. (Chris Jackson/Getty Images)
Neither Charles nor Camilla were hit by the eggs.
The royals kept calm and carried on in those situations too.
The protesters in Milton Keynes also reportedly plan to demonstrate at King Charles' coronation. (Max Mumby/Indigo/Getty Images)
The monarchy’s relevancy has faced new scrutiny since the queen's death in September after reigning for 70 years and Charles has signaled he may want to slim down or streamline it.