Probably not. SSRS itself doesn't need a license. You get it with SQL. However SSRS requires a database and therefore a SQL instance to host the database. So if you're just hosting the SSRS components, and not the databases, on another server then your existing SQL license is fine. If you want SSRS completely on a different server, including the reporting database needed to support SSRS then you'll need a SQL license for just that aspect. In my experience most people host the SSRS databases on their standard SQL Server instance and SSRS on another server for performance reasons. A single SQL license is fine for this.
Of course you still need to license the VM OS itself. I assume you already have a valid license for that. So you can host SSRS services on any machine you want.