Sure. Some beasts people haven't tried to tame. In fact, I would say the majority of them are that way, especially since the beasts get more and more wild the further from human civilization, and there are probably many beasts people didn't know about.

I'm really imagining this world as being highly fortified but highly isolated cities, in the middle of wild territory filled to the brim with wild beasts and strange plants. The cities are ancient, originally built upon crossing ley lines of safety that prevent the most absurd of the beasts from drawing close with harmful intentions. That is why it is such a massive undertaking for your character to leave the city and try and go somewhere else.

I think just humans would probably be for the best. 

The way I'm kind of seeing magic in this world is as specific traits that are linked to individual species, rather than having some aether pool that anyone or anything can draw from and shape in any way. So, since humans don't have any of those specific traits, they probably wouldn't really believe in magic, although I could see superstition running rampant.