My advice. Don't use a compressor. While it is possible to create the conditions where it's safe to use, more often than not, static generated as the air passes through the line, dirt and moisture can all be problems. It can also jam dust further in rather than removing it.
If your computer needs a clean, use a brush (one like this will be ESD safe, if you use a regular brush, keep it away from electronics) and a vacuum cleaner. Saved cleaning up the dust afterwards. Filters and heat sinks that can be removed from the system can be hit with the air. Just discharge them when you're done.