[winter_blue]

Anti-particles and particles instantly annihilate each other on contact, so anti-particles cannot not exist in our world besides for brief moments.

There's a theory that half of the universe is made of anti-particles (and the other half composed of regular particles). So you could say that the half we inhibit has few anti-particles in it.

See: https://en.wikipedia.org/wiki/Annihilation

[averagewall]

They're also created all the time by radioactive decay which happens in common building materials. So yes, they'll be flying around your room now, but not going much further than that.