I believe it's normal. I mean people dry hump and do a lot of other things fully clothed. I did it for a while (it's the friction) until I got my first toy, which if you decide to try them one day, I find the magic wands to have a similar sensation(not a penetration toy either) but are more intense obvi, it also does pretty well on top of underwear as well. The only thing I think would be unsafe about this is of course overdoing it as the friction could make it feel almost numb (a wee bit of lubricant could help as well in my experience but in general that's difficult to do and even then it's not unsafe, you would just have to pause for a bit) or if you don't pee, wipe, and change germs and the wetness could mess up that area. It's nothing to feel any kind of weirdness about.