Taggy. I'm assuming you mean proper live bands rather than just the entertainment and karaoke-style stuff that is widely available. Live acts tend to be one-offs as opposed to regular events in any bars that have them. Irish Tavern in the port has a rock evening, but even that I'm not sure of regularity.
The best live music tends to be available during fiesta weeks, much of it in the old town.
The music bars themselves tend to specialise in DJs rather than live acts.
If you venture to Puerto Pollensa, Mulligans and Olivers have both had live music evenings this season, but this could all change next season.

Thank you Andrew

Best Regards - Taggy