if you AV is telling you that you have a virus it is most likely a false positive. AVG is reportedly a botched application for Mac and AV as a whole on the Mac is generally more trouble than it is worth at this time.
remove all traces of any AV and any "Clean my Mac" applications you may have
since you most likely do not have a virus your system does not need to be restored. Whoever told you that you do have a virus will need to back up that statement with some proof. Is your computer in a place where someone other than yourself could sit at it and install a rootkit from directly on the keyboard or over a remote session with your credentials? Have you given someone your credentials? have you knowingly installed a rootkit recently?
While I don't fully endorse it you may want to try this to get a second opinion and ONLY if you answered yes to any of the questions I asked in the paragraph above. Again this is not a piece of software I use on the mac but historically have used on Windows and have some faith in the manufacturer. To that extent I do not claim to know the full extent of how well it works on mac or if there would be further ramifications by installing it. I offer it a something to mull over and make your own decision after doing some research.
http://www.eset.com/int/support/rootkit-detector/
if the system is exhibiting signs of problematic behavior you may submit an etrecheck report to determine what the actual cause may be
http://www.etresoft.com/etrecheck
In the mean tine if a problem persists with system functionality.
reset your SMC
https://support.apple.com/en-us/HT201295
rest your PRAM
How to Reset NVRAM on your Mac - Apple Support