some one logs into my fb account when im on it, can i find out who?

[Kim G]

Yes, you can. When you go into Facebook, go to Account > Account Settings, then go down to 'account security'. There is an option for facebook to alert you when another computer or device is accessing your account. You can give your own computer a "name" so you know the difference between which is your computer and which is the unfamiliar computer.
This won't tell you "who" is accessing the account but it will tell you the computer details eg browser, approximate location, operating system.
If you don't get any alerts, then the chat box is likely an error with your own browser. Try seeing if it happens with a different browser.
Best thing to do is to change your password.