If by "carnivore" you mean the mammals in the class Carnivora, the only one I know of is the golden jackal (Canis aureus), which occasionally grows a small hornlike growth at the back of its skull. Usually it's covered by fur and not easily seen. read more
Though in general, “horns” in carnivores tend to be more for show, rather than weapons. Extant ones include some lizards (horned lizards, chameleons, etc.), fish (cowfishes, horn sharks, etc.), frogs, snakes, the Cuban crocodile, and a lot of invertebrates. read more
I don't count bug-eating horned lizards. Nor cattle that are duped into eating feed made from the ground remains of kin. read more
However, there are many definitions of horns (some only consider the horns in Artiodactyla to be"true" horns), so you need to be specific in what you are asking for. Used casually, the antlers of Cervids or other similar structures, are often considered as horns. read more