That kind of depends of what you mean.
If you don't want unwanted guests on the webpage that invites people to log on the the Farm, the answer is no. Anyone with an internet connection could connect to the site.
You can block access to the farm based on security group membership. Say, for example, you're publishing applications. Word should be accesible for all and Publisher shouldn't. Under the properties of the published application you can specify who can access the application.
As I think off it, there are ways in which you can hide you're webpage. If the site is hosted in the companies DMZ, you can create access lists on the outer firewall which would specify MAC addresses of machine which are allowed through, for example. You can also incorperate software like RSA SecuRemote in Citrix. Users now need a smartcard to access the site in the first place.