There's not a lot of visible difference between a mind map and a navigation model – they are both "boxes and arrows" that connect objects in a structure. The use of them and the information they contain are very different, in my opinion. A mind map usually represents a conceptual model of a domain, and how information relates to each other. I usually frame my mind maps to be aligned to how users think of a particular domain. A nav model is a more literal representation of the links between screens (user interfaces).
You can make a nav model be aligned with a mind map, but it could be hard to understand, and you may be trying to align two things that don't really work together well (conceptual vs. literal).