Since this question doesn't have a definitive answer yet, I suppose I'll expand on my comment above.
As Ankit Sharma explains, Garlic Jr. is from the Makyo Star. However, I find it doubtful that Emperor Pilaf is also from the Makyo Star. Emperor Pilaf was the first villain introduced in Dragon Ball, when Goku was still a child, before we even knew that Goku was an alien (let alone Piccolo, who wasn't introduced until much later). All the material involving Garlic Jr. is anime-original and dates to long after the start of the manga, whereas Emperor Pilaf is Akira Toriyama's own creation and was introduced right at the start.
So why do they look alike? I think it's just a coincidence. As Zibbobz mentions in comments, this would make Emperor Pilaf some kind of Earth creature. (Considering all the weird creatures that live on "Earth" in the Dragon Ball universe, this isn't too hard to accept.) The Dragon Ball manga went on for a long time, and Toriyama himself occasionally used slightly tweaked versions of his earlier designs; that's why Emperor Pilaf and Piccolo look so much alike. The animators who designed Garlic Jr. had to come up with their own design, but also make sure it was consistent with Toriyama's art style. They chose to tweak Emperor Pilaf and Piccolo by changing the color and removing the antennae, probably to maintain a recognizable look.
The animators did something similar in the movies: Turles, the villain of The Tree of Might, looks exactly like Goku, for no reason I can remember. Bardock, Goku's blood father, introduced in Bardock - The Father of Goku, is also an exact copy of Goku's appearance (and even shares the same voice actor in the Japanese version). Toriyama's character designs, especially for non-human characters like these two, have a very distinctive look. It's plausible that the animators decided to play it safe and copy his designs, instead of taking their chances and trying to replicate his unique style.