Well..there certainly aren't in Star Trek; but there aren't any Christians in Star Trek, either. Rodenberry (the creator of Star Trek) explicitly said that by the time of Star Trek: The Next Generation mankind had "grown out" of religion, and that belief in God in the 24th Century was virtually unknown.
When J. Michael Straczynski created the series "Babylon 5" in the '90s, he made it a point to illustrate the religion was alive and well in his version of the 23rd Century, and had characters who were Christian and Jewish. In the background, other characters were occasionally mentioned as being Muslim or atheist.
Interesting tidbit: Roddenberry was an atheist, as is Straczynski, but the latter seems to have a much more realistic view of mankind.
Wierdenberry also claimed to have slept with nearly every female guest on the show