If you mean your IP address and identified means can be reached, then yes.
However, most people get a dynamically assigned IP address from their ISP when they log into the service which will only last for that session. Some people have a fixed IP (e.g. Pipex ADSL users) which never changes.
There are good and bad points about both. However please install and use a firewall to protect yourself from the bad guys (who probably are not interested in you at all) and use antivirus software to protect yourself from the really bad guys who don't give a damn about who they hurt.