Moisture and temperature are the 2 means that need to be present in order for mold to accummulate.
If the ceiling is 'peaked' where the mold is growing, heat and moisture will 'collect' there and mold will form. Sometimes, all that's needed is to better circulate the air. Initially, I don't suspect a leak because I think you would have more damage as time wears on. But, only a closer inspection of the ceiling there will tell you if you have a water problem.
To clean this, put on a pair of gloves AND wear protective eyewear. (You will be working above your head and dont' want to get any of the spray cleaner in your eyes!) You'll want to mix some bleach with water in a spray bottle and spray it on. Wait a few minutes and try to 'dab' it off. Beings that you have a textured ceiling, you can't rub the area. If you notice that the mold 'disappears' (AFTER waiting a few minutes) without having to dab the ceiling, then don't dab it. Be careful and take your time so you don't ruin your textured ceiling! Hopefully, your ceiling is white. Try a 50-50 mix and see what happens. And try it on a small area first.
My best to ya and hope this helps.
PS: BEFORE you do any cleaning, if there's any access to the 'space' above the damaged area, have someone take a look to see if there are any signs of moisture. If there are, fix that first before you clean the ceiling. (Otherwise, you'll be back 'at it' again in due time!) They should see water rings perhaps dry rot if there was water up there. You can gently 'push' on the ceiling to see if it's soft too.