Perth Theatre, which re-opened to the public on Saturday, was evacuated at around 4pm during a pantomime performance of Aladdin.
The threatre has undergone a £16.6m refurbishment.
Scottish Fire and Rescue Service attended the incident but the cause of the raised fire alarm was unknown.
Deputy First Minister John Swinney was in the evacuated audience at Perth Threatre.
Mr Sweeney represents Perthshire North at Holyrood.
He tweeted: “Great to be at the opening of the refurbished #Perth Theatre @HorsecrossPerth - a work of art. Fabulous performance of Aladdin. Added extra of fire alarm and cast brought back on stage by @fire_scot. Hilarious.”