Hit it with a hammer, and if that doesn't work, get a bigger one.
Seriously, though, if it's a built-in keyboard, I see 2 possibilities:
One: Kaz is right, and you're hitting the track pad.
Two: Bad/exposed wiring. Take it back to the store or take it to a pro to fix.
In my experience, problems like these can never be fixed, unless it's something crazy simple. My advice is to return it and get a new one.
(unless you ARE hitting the pad, in which case you need to return your hands to the manufacturer)
Want to help a brother out? Click
Here and hit "Start Generating"!
"Argh! He's not gonna get away with this!"