What do you mean by a pop-up?
There is a way to show/hide text etc with a button - but be aware that this functionality is NOT fully supported by most epub readers.
If you want to know more then try Steve Werners tip for creating buttons which can be found here : http://indesignsecrets.com/creating-a-two-function-button-for-interactive-pdf-or-swf.php
Jump to the bottom as he revises his solution.
If you ever find an epub reader that works on Android for this solution let me know please
thanks Howard for your reply.