Not necessarily. It
could be a sign that they are dating or might want to date each other, but they could also just be really good friends.
It's been awhile, but I've gone to the movies with just a (female) friend of mine, just as something to do so we can hang out, and it's never turned into something more :P
There are a lot of other factors that determine whether two people are interested in dating, and while spending time together (mostly) alone is one of them, it's not definitive.
Hope this helped a bit
