Yes, and no. A relay owner can decide to not relay your notes, but there are other relays. You can also host your own relay.

Individuals can block/mute you if they don't want to see your posts.

So, if you're enough of a jerkwad, everyone mutes you, and all relay owners ignore you, you'll be close to "banned". 

 I just realized that a typo in my first reply screwed up what I was saying. Nostr DOESN'T handle privacy... which is why you would need Tor, VPN, etc.