In this study, we describe the design of a Mixed Reality (MR) portal system with an AI companion. Our system allows the user to enter various virtual portals that are placed in the real world via an MR headset. Each portal contains a virtual world with a different theme and settings. The user can explore and perform activities relating to the virtual world theme. The AI companion will accompany the user and provide guidance. We use Natural Language Processing (NLP) for the AI companion to provide conversational between the user and the AI companion. The user can ask the AI companion about the specific virtual world. In addition, the AI companion is also able to interact with certain objects inside the virtual world. The goal of this MR portal system is to provide an educational application that is interactive and immersive. We provide the initial proof of concept implementation of the system. This study also highlights the technical challenges and solutions in integrating the AI companion that understands the context of each virtual world.