Can you take a screenshot next time it happens and include it in a reply so we can see it? You don't make clear what it is that's prompting you.
A thought if it is Mcafee saying an update came in and is asking for a restart maybe this thread might help.
Could you please provide us the below information;
What is the operating system of the computer ?
What Service pack ?
Check if your computer has all the important windows updates installed ? - If not Open Internet explorer - Click Tools - click on Windows Updates