Question: I heard that it is possible for Dharma cultivators to have supernormal powers. How do they arise?
Answer: Some non-Dharma cultivators have such powers too – as a result of having trained the mind in a past life, and/or ‘accidentally’ sharpening the mind through meditative practices in this life.
Question: I also heard that these are meant for them to better help others?
Answer: Such powers have no fixed purpose, up to the person to ab/use, and some do abuse them for personal benefit, for gain and fame. (Again, note that supernormal powers can be attained through non-Buddhist practices too, which might not be guided by Buddhist ethical considerations.)
Question: After they possess such powers, are they still considered normal human beings?
Answer: As long as they are not enlightened yet, they are still human beings – just with some supernormal powers. Supernormal powers attained without enough compassion and wisdom will lead to creation of magnified negative karma as there will more and easier ways to do evil. One can become ‘demonic’. In this sense, one can lose humanity (and the precious human rebirth), if a lower rebirth results.
As such, it is more important to cultivate compassion and wisdom than supernormal powers, which might naturally arise when training the mind.
To look forward to such powers instead of focusing on the power of compassion and wisdom is to miss the key objectives of the Dharma – for learning and practising towards liberation for one and all. Pining for powers is an expression of worldly greed, that can disguise itself as ‘pure’ spiritual motivation.
Note that the Buddha forbade the open display of supernormal powers for no good reason, lest it attracts attention for wrong reasons. Those who do so are going against the Buddha’s teachings. They might not even have actual powers; only pretending to have them. What we should attract others with is good moral conduct and sound understanding of the Dharma.
Even if with some powers, they can also give rise to pride and the illusion of being enlightened, thus distracting oneself from further Dharma learning and practice, while deceiving others.