Radio service using battery
Battery stats always lists consumers. If the mentioned entry would refer to "fm radio", it had listed the corresponding app as consumer.

You must be aware that the term "radio" is ambiguous here. It stands as an abbreviation for "radio waves", which in fact are used by "fm radio" – but also for communications using the cellular network. The latter is what you're seeing references as "radio" in the battery stats on some devices. Different devices might use different terms here, so a screenshot helps identifying the "item" by its associated symbol/icon, see e.g. What is Cell standby and how can I keep it from eating my battery?

With that link, I've also named how other devices might refer to this ("cell standby"). If your symbol looks similar to the one shown in the screenshot there, that would confirm what I've written here (note that it might look a little different on your device, not only due to a different manufacturer – but also due to the fact the screenshot on the linked question was taken with Android 2.3 ;)