An aromatic vinyl copolymer is a polymer of a reaction mixture including: an aromatic vinyl compound; a vinyl cyanide compound; a silicone compound having at least two unsaturated reactive groups; and a C4 to C20 linear or branched alkyl group-containing acrylic compound. A thermoplastic resin composition including the aromatic vinyl copolymer can have excellent matting properties, impact resistance, flowability, and balance therebetween.