See the answers to this question, which do not discuss non-rabbinic Judaism specifically, but whose points can be expanded to them. My own answer there says:
The question asks:
1. Are questions asked from the perspective of, or about, a particular movement on-topic? Always? Only halachic movements like Conservative? Never; this is an Orthodox site?
Monica Cellio's answer (hereinafter "MC" (just for ease and WADR)):
Asking questions about, or from the perspective of, any Jewish movement or community should be permitted.
I agree in general, but we need a question to be answerable and (as the FAQ list says) "for those who base their lives on Jewish law and tradition and anyone interested in learning more".
Thus, it cannot be "Can someone explain this practice of Mysect Judaism?" where Mysect Judaism lacks Jewish-tradition-based sources that discuss the question.
As far as I can tell from what little I know about Karaite Judaism, that last paragraph applies to its practices directly where such practices differ from mainstream Judaism's, or at least to most such. Definitely this can be decided on a case-by-case basis, though.
http://meta.judaism.stackexchange.com/a/472. However, see
http://judaism.stackexchange.com/q/23475, "How do Karaites pray?", from January, which has not been closed as off-topic; according to what I write above it should be, but I await others' views in answers to this question.
I'm guessing you asked this as a followup-to the recent question "Are there any Jewish sects which regard the Oral Law… as unlawful addition to the religion? If yes who are they and what are their beliefs?". The last part of that ("what are their beliefs?") is off-topic IMO per what I wrote above. The rest of it is, from the perspective of the asker, not off-topic, since it asks about something that the asker doesn't know lacks Judaism sources; a good answer might be "yes, but such is not generally considered Judaism; the most prominent example is the Karaites" with a link to more information.