Depending on whether you run OS X Lion or Snow Leopard, download these updates if you haven't:
These will automatically remove all variants of the Flashback malware on your Mac. If that worked, hooray, nothing to worry about.
If that didn't stop the processes, you have several options. You could, first of all, disable Java altogether by opening Applications/Utilities/Java Preferences.app and deselecting all versions of the Java VM. In my experience, you often won't need Java anyway.
If you don't want to do that, you can try to narrow down which process called the Java processes. Open up a terminal and enter:
ps auwwx | grep java | grep -v grep
If there's anything listed, check the corresponding user and the command line (in the last column). Do you notice anything unusual?
From that command line, you should be able to identify the source of these processes. Then, it's just a matter of either uninstalling that particular program or letting it run (in case it's any vital process you just forgot about).