If you have a way of connecting your Mac with your TV, you may not need an Apple TV. That would depend on what connections each device has and the distance between them.
To be honest, even if you have the correct connections and they aren't that far apart, it's much more convenient to use an Apple TV.
You may need a cable that connects HDMI to whatever type of connection your Mac has, so far as I'm aware only the Mac Mini has an HDMI output.
Also consider distance, I'd be inclined to go no further than 10 meters, anything longer and I'd want to know if the cable meets compliance standards and see it's certificate.