Hard to say, you've given us so little information. Can you tell us a bit more about your MacBook Pro? Specifically, what version of OS X are you using, how old is the machine, what browser are you using and what sites do you experience the slowness on?
You may also want to run a speedtest.net test to check your bandwidth. And if it's a wireless connection, try connecting via Ethernet to your wireless router instead and see if the problem persists.