Yes, it is fine to ask about mathematics as it relates to non-mathematics areas. There are, for example, many questions on MSE relating to physics, economics, and computer science. In fact, I would encourage you to post such questions. I find it personally interesting to see how mathematics is used in various contexts.
The general rule is that your question should be about the mathematical part. You can/should explain the context, but the question itself should be about the mathematics. If you, for example, have a mathematical model that relates to economics and you have questions about the model, then this is the right site. If your question is about the economic principles behind the model or interpretations, then another site might be more appropriate. There will, of course, always be grey areas.