How heavy is that antenna? I've got a big ole roof mount and it's probably... 10 lbs max. And unless your walls are made of notebook paper you can hang a fair bit of weight with the right anchors.

You're first option is just a basic picture hanger available in any hardware or big box Wal Mart type store. It costs a couple bucks.

There is also a Gorilla Hook. You don't even need any tools. I don't know that these are any better than the picture hangers, but they're kind of cool.

With either of those, it's a small hole that you can plug with either a tiny bit of spackle or toothpaste (yeah, seriously). Then if you really want to hide it, you go get a paint sample for a few bucks and paint over it. You just need a tiny, tiny bit of paint though. Paint too big a patch and it can be obvious that it was done.

Next up are drywall anchors. I use the metal ones, These are usually just for shelves or big mirrors and what not. They're overkill for what you need.

Then there's the old "find a stud and drive a screw in" method. Properly installed, you can mount a pull up bar doing that. So that's really overkill.