You can install it on as many computers as you want, it just probably won't activate on more than one or two.
This question could easily be answered by a slight variation on the RTFM adage. In this case RTFL, or Read The Fine License. You know that big long thing full of legalese that you have to click "I Agree" to? Sometimes tick a box, THEN click "I Agree"... Well, it will tell you exactly how many concurrent installations you are permitted. Almost always, it's one and only one. So, you can either buy another copy of NAV if that's the case, or you can use a free alternative such as AVG Free or Avast.
I just got norton antivirus and I was wondering if I can install it on both of my computers. Thanks!