It happens to me at work and is annoying as hell. I assume it's a kind of nervous thing, as whilst I have no trouble putting myself out there in terms of attention on me, I'm naturally quite a nervous person. Doesn't happen when I'm in regular situations with friends or my better half.
It can be tempting to try and mask it, wearing jumpers over shirts etc, but I've found that masking it just makes it a bigger deal in my head.
Just remind yourself: People sweat. It's normal. Some rarely sweat, some sweat often. Unless you're reeking, and nervous sweat on people who shower every day rarely are like this, other people just have to deal with it.