Dear Kevin,

Thanks for the question.

No, it is not OK.

The Catechism tells us:

CCC 2116 "All forms of divination are to be rejected: recourse to Satan or demons, conjuring up the dead or other practices falsely supposed to ‘unveil' the future. Consulting horoscopes, astrology, palm reading, interpretation of omens and lots, the phenomena of clairvoyance, and recourse to mediums all conceal a desire for power over time, history, and, in the last analysis, other human beings, as well as a wish to conciliate hidden powers. They contradict the honor, respect, and loving fear that we owe to God alone."

You said:
there are people who do magical practices and they also believe in God, and at times, use their power to serve God.

Matthew 6:24 tells us:

No man can serve two masters: for either he will hate the one, and love the other; or else he will hold to the one, and despise the other. Ye cannot serve God and mammon.

For short: you cannot serve God and Magic.

You also have to ask the question:

• How can someone who is involved in magical practices, which displease God, serve that God?
  

I would differentiate between:

magic tricks done by young boys or professional magicians based on optical illusions for crowd entertainment

from

black magic which leads to the occult.

Those done by the professional entertainer I wouldn't worry about nor the young boy as it is usually a passing interest.

My colleagues will reply if they have a differing opinion on this.

Hope this helps,

Mike