Could you provide a pic for a positive ID?
Either way here's what you can do to take care of the aiptasia or majano anemones (2 most common pest anemones):
If the rock where the anemone is can be removed, use a lighter or cooking torch to burn it off. This works best
imo\ime.
If the rock can't be removed, you can inject various things into the anemone with a syringe:
kalk paste, hot lemon juice. There are also other commercial products you can use: joe's juice, aiptasia X etc.