Most likely there's an intermittent short with your keyboard, and it needs to be replaced, or even just have the ribbon cable reseated. Since reseating the cable would involve at least partial disassembly of the unit, you would get into potential warranty voiding areas, so I can't recommend you try this on your own unless you're willing to accept the potential consequences.
If you're within the return period of wherever you purchased the unit, you can always go that route, otherwise I would recommend sending it in for service.
http://support.asus.com/ will help you get started. If there's an authorized service center in your area, you can always take your unit to them and let them try reseating the cable to see if it helps.
