Can I have tattoo if my skin having keloid?

Be careful. Any form of trauma to the skin (include getting a tattoo) can cause a keloid if you are keloid prone. It is a hard question to answer. A tattoo rarely causes keloids, but it is certainly possible. Err on the side of caution.
Keloid. If you have a tendency to develop keloids, it can possibly form over the area of tattoo.