The Coastguard was alerted but the emergency services were not required after the blaze broke out in the engine room of the Saga Sapphire at around 10am yesterday.
Repairs were carried out and the ship was expected to resume its journey today.
A Saga spokesman said it was a small fire and nobody had been injured. He said: "This was quickly and professionally dealt with by the crew."
"The ship is anchored, in fine weather, off the Isle of Mull whilst the damaged electrical panel is repaired and tested. Our priority is always to make sure our passengers and crew are safe and well. We have 589 passengers and the total number of people on board is 1008."