6G networks will take the digital services offered by 5G to a whole new level with considerably higher bit rates, lower latency, and ultra-re-liability. However, the security of these systems is crucial to fulfill the promise of 6G. A critical element of this requirement is the efficient and pervasive protection of 6G infrastructure and services. In this article, we propose Moving Target Defense (MTD) as a key proactive defense element and elaborate on how it can be integrated into beyond 5G systems. We also present the standardization perspective, the relevant research challenges, and future research directions.