Quote from roadrunner:
If you're lucky it's some kind of shortcut in the wires. You'd cleanse the keyboard using calcium free water (buy some at your local garage), wash the beer stains off of the keyboard layers and let them dry. Be sure there is no water between the filaments when reattaching the keyboard, you might cause even more severe shortcuts!!
Another possibility is that the beer corroded the wires, in this case you'll probably see the wires on the filaments turned from silverish to grey/black, in this case you need a replacement keyboard or just live with the current situation.
How long would you let the keyboard dry for after washing it with the water?