This is a well-known question that kids ask when riding somewhere in a car, on a plane, etc. It means "Are we going to arrive at our destination soon?"

Sometimes when they want to annoy their parents, kids will ask "Are we there yet?" over and over again:

Child: Are we there yet?

Parent: No.

Child: Are we there yet?

Parent: No.

Child: Are we there yet?

Parent: No! And stop asking!

Adults will sometimes jokingly ask this question to their friends, spouses, brothers & sisters, etc. who they are riding with.