It's a Keychain thing. You can find the Keychain app in Applications > Utilities > Keychain Access. Or spotlight for it. There you can view the different keychains that are set and troubleshoot.
I had a similar issue where whenever I opened Safari I was prompted to enter my Keychain password. In my case I believe my Keychain got corrupted and I solved it by deleting my Keychain file and starting from scratch.
Keep in mind if you do this you will have to re-enter all the passwords you currently have stored in your Keychain.
If you want to delete you Keychain go to: HD > Users > YOUR USER ID > Library > Keychains