Yes , my sister said once that she sees the wind. I regret what I said next for I told her "No, that's impossible" and *I'M* supposed to be the open-minded one.
So anyways. Lot's of things are invisible. God for example. And I see God just fine. Some people go their whole lives never seeing it. I also know how girls think, and I am a guy, and a lot of guys go their entire lives genuinely not understanding women (And hurting them in the process).
That may seem far-fetched to you, but seeing the air is far-fetched to me.
Shamanism is ALL about seeing invisible things, and then being able to translate that into the ordinary/visible/physical world, and the going back-and-forth (with integrity) between the visible and invisible worlds. That *is* shamanism. So to answer your question: Yes that is normal.
Next time you know there is someone invisible there, ASK "Who are you?" and wait for an answer. You'll know it if they have replied or not.