If you can move your cursor, the computer is not frozen.

What operating system is your computer running?
What is on your screen when you come back? Is it completely black? How do you "unfreeze" it? What appears on your screen when the "freeze" is over?

I have a similar computer, Satellite Pro, 2 gigabyte RAM, 250GB HD and same CPU. I've never had the problem, and it sounds software related, as in a virus.