What is it?
nopdb.exe is a file associated with Symantec's Norton SystemWorks.

What does it do?
nopdb.exe might be a scheduling agent for a program called Speed Disk that is included in SystemWorks.

According to Symantec:
Speed Disk improves system performance by reorganizing the contents of your disk.

More info
You can read more about Norton SystemWorks at www.symantec.com

It is popular opinion that Speed Disk consumes resources and slows down read write access to the hard drive that it is working on. Apparently it is much like MS Defrag. I recommended that you reschedule the application to run at a time that will not inconvenience you by any system slowdowns it might cause.

At the time of this writing I did not find any significant risk related to viruses or adware/spyware related to the file. You will want to keep an eye on this google search look for any association of nopdb.exe with viruses, spyware or adware.