Replying to Macbook help

I have a macbook pro and this is my first apple experience. After about 2 minutes of not touching the keyboard or mouse, the computer screen gets a little dimmer. It doesnt go completly black, it just loses some brightness. Its just annoying when this happens when I'm reading something and I don't need to use the keyboard or mouse. Where can I shut this off. I've already set my energy saving settings so the computer won't sleep for two hours. Thanks for your help.