East Sussex Fire and Rescue Service said it was called to the branch in Lottbridge Drove at 6.35pm last night (Thursday, June 30).
A fire service spokesperson added: “McDonald's staff and customers were safely evacuated.
"Firefighters tackled the accidental fire and made the restaurant safe. Incident closed at 7pm.”
A spokesperson from McDonald’s added, “Our Lottbridge Drove restaurant temporarily closed yesterday at 6.30pm after a small electrical fire.
"All of our people and customers were evacuated safely and emergency services attended to extinguish the fire.
"The issue has now been resolved and the restaurant reopened to the public last night.”