What's going on with my imac?

Everyday when i'm on my imac all of a sudden my computer goes back to the previous page. This happens about 3 times when i'm browsing the internet. I have no idea why it's doing that! I'm a little freaked out because a couple weeks ago an "apple security center" malware thing popped up. I found out that it was trying to give me a virus so i didn't download anything. Also, a macguard malware thing came up too. So, can anyone tell me why my imac goes back to previous pages sometimes? I've only had my imac osx for about 1 year.

Could this be happening perhaps while you are attempting to post in a forum? I have had it happen here a few times but did not go looking for an answer till I read your question.

In my case I think I was accidentally hitting the Delete key after having clicked outside of the text entry box. I knew the Delete key was the culprit but didn't realize why it only happened sometimes till I read this How to disable backspace/delete go back in Safari?