If you have a computer that is not connected to the internet then you should still be running an antivirus program on it to protect yourself against viruses. There are sufficient ways for a computer not connected to the internet to get infected that you would be stupid not to.
Unfortunately, keeping your antivirus up to date on a computer without an internet connection is much more difficult than for one that can connect. It is not impossible though because many of the antivirus sites provide an option that you can use to download the latest signature file. You can use any internet connected computer to download the file and write it to a disk or CD. You can then install the signature file update into the antivirus program on your computer that doesn't have an internet connection using the file that you downloaded.
So which antivirus software offers this option and where do you go to download the latest signature file? Well here are links to some of them.
This article written by Stephen Chapman, Felgall Pty Ltd.