Excessive FPS drops

Hello, I recently got a new computer and while running around at a solid 120-130 FPS, my game will randomly drop to the 10-20 range for a few seconds. It's not to big a deal but since my computer is very top of the line, I'm wonder why it does this.....Anyone like to fill me in?

Windows 7 Home Premium 64-bit
AMD Phenom II X4 965 Processor
4 GB RAM
ATI Radeon HD 5850 1 GB Video RAM

(I run the game at Very High graphic setting, 1920x1080 resolution)