Not sure what kapfundestanley is talking about; but probably posted to the wrong post.
As opc.three said, why would you want to do that?
Installing a service pack will alter the master database and perhaps the msdb. If you try to install the SP, it may fail with an error about a "database currently being restored", but I really wouldn't want to try this on anything other than an experimental sql box that I use for "breaking" sql or attempting such a thing that you may be considering.
You can't wait for a restore to complete to install the SP?