|It depends on the bug. If they visit the same site both computers may be infected. |
If one computer gets a virus the other may, in time, get infected if nothing is done to remove the bug.
Most generally, virus attacks are welcomed in by clicking a button or visiting a page on the internet, or email. Other bugs look for open ports and migrate through that to infect other machines.
Generally speaking, there is a small chance of the other computer getting the same bug in your case. Most antivirus software will catch them before they can get in.