I used to live in a place where humidity was routinely 80%+ in the summer. My computer worked just fine. In an interesting fluke, if you were planning on working on the computer, higher humidity is actually better since static build-up is harder to achieve in humid environments.
Humidity is only corrosive if there are other things in the air that make it so. If you live next to the ocean, then yes, things rust faster because there's also salt. However, most of the exposed metal parts in a computer use corrosion resistant metals. Like gold plating is used on the contacts of expansion cards and some connectors. It's only a problem if things that are normally covered get exposed.