My forums currently need to go under heavy development. Is there anyway so I can lock it so no one can get on besides admins?

Seems you have just set up your forums. If you are using mist forums domain. I would just not publicly release the URL until you are finished. Although if you are using a custom domain, you could point the domain to a Pastebin saying "Forums are closed due to maintenance". 

This feature is not currently available. Moving to suggestions for further review.