Heat grill.
Combine the mayonnaise, sour cream, feta cheese, minced garlic clove, chili powder and cilantro and set aside.
Cook ears of corn on the grill, about 8-10 minutes (or until cooked), rotating every couple minutes to char all side of the ears.
With a spatula or large spoon, lightly cover each ear with the cheese mixture. Sprinkle with chili powder and serve immediately.