Welcome to Apple Discussions!
Is your question regarding Time Machine? If it is, disable Time Machine until such time you need to backup again. Apple menu -> System Preferences -> Time Machine. Otherwise, if it is some other application making temporary files, quit that application. Temporary files usually are cleaned up by the application when they are quit. If you are running out of space, see my FAQ*:
http://www.macmaps.com/diskfull.html
- * Links to my pages may give me compensation.