The concept augmented realie is used to describe a system that supplements reality by adding virtual objects into a real-world view.This paper describes a flexible mobile code approach that we can use to implement ubiquitous, active, and mobile augmented reality systems.We will concentrate primarily on solving the problem of how to acquire the data for the virtual objects in a way that will be flexible and expandable enough to be used in truly ubiquitous computer systems.To clarify the concept, we will present an example system that provides virtual user interfaces for various real-world objects.This paper suggests that the mobile code approach offers a relatively simple solution that is flexible, scales well, and does not require the computing equipment attached to the real-world objects to be excessively complicated.We can use the same mobile code approach in applications that provide only simple descriptions of the real-world objects and in complex applications that allow the user to manipulate real-world objects via virtual user interfaces that exist only in augmented reality.Our approach also supports active augmented reality, in which the virtual objects can react to the real-world events.