If it's a small area, use a solution of one-quarter part bleach and three-quarters parts water. Wear gloves and wipe it down. The bleach should kill the mold. This process will do a great job as long as it's surface mold.
You need to find out where the mold is coming from before it spreads to other areas. You may have a small leak somewhere that isn't enough to come through, but may cause mildew and mold inside the ceiling.
https://m.wikihow.com/Remove-Ceiling-Mold
https://www.wikihow.com/Remove-Ceiling-Mold
If it's a small area, use a solution of one-quarter part bleach and three-quarters parts water. Wear gloves and wipe it down. The bleach should kill the mold. This process will do a great job as long as it's surface mold.
I had a small area (about the size of a saucer) and used a bleach/water mixture in a spray bottle. It worked!
You need to find out where the mold is coming from before it spreads to other areas. You may have a small leak somewhere that isn't enough to come through, but may cause mildew and mold inside the ceiling.