This paper studies how to extend the concept of active object into a structure of agent. It first discusses the requirements for autonomous agents that are not covered by simple active objects. We propose then the extension of the single behavior of an active object into a set of behaviors with a meta-behavior scheduling their activities. To make a concrete proposal based on these ideas we describe how we extended a platform of active objects, named {\it Actalk}, into a generic multi-agent platform, named {\it DIMA}. We discuss how this extension has been implemented. We finally report on the application of {\it DIMA} to model economic agent evolution.