Currently Being ModeratedDec 9, 2012 3:10 AM (in response to ajsy28)
Sounds as if it's a hardware issue - are you still under warranty? If so, take your machine to your local Apple Store or an AASP and have them take a look at the screen - it may need replacing. Even if you're not under warranty and it's something that bothers you, you could always pay to get the screen replaced. I doubt that it's a Mountain Lion issue.