The thought of being executed over music seems absolutely ridiculous to me but this is Iran so what do you expect. People have absolutely no freedom of expression in Iran. Iran controls everything their citizens do. They control their personal and public lives. I really hope they won't get executed.
The Iranian band "Confess" should not have been arrested, nor should it be facing execution for expressing themselves through their music. According to several articles online, they could face the death penalty if found guilty of blasphemy and of running an illegal band. This hasn't been an isolated event regarding banning music in Iran.
The Iranian regime pulls this sort of thing pretty much on a weekly basis, merely with victims of a lower profile (not that a metal band that nobody but Iranians has ever heard of before this happened is that high profile either). I'm honestly not sure why they bother, given the amount of domestic trouble this sort of behavior inevitably produces, for no benefit I can discern. I can understand arresting or disappearing say, political dissidents (not that I support it, but at least I get the rationale driving the people who do). A metal band on the other hand, is not terribly likely to serve as a rallying point for revolutionaries; that is, unless somebody decides to make martyrs of them.
It's ridiculous some of the customs and rules that they have over in the Middle Eastern Countries. These poor people can't even enjoy themselves and it's disgusting that people are treated like this. I know that I would be lost without my music and if I couldn't listen to a particular genre I'd probably take a stand against the government.