Conference; withdraw submission before results notification In conferences, especially in computer science domain; is it ethical, accepted and legal to withdraw a submission before the results notification/announcement? 

Anyway, what if it has been just accepted!
In certain cases, e.g., when you found a serious error in your paper, it is very acceptable to withdraw the paper, as soon as you possible. Paper can be withdrawn even if accepted. It is better to withdraw as soon as possible, to allow the conference to accept other papers or to avoid the overhead of reviewing the paper. 

Even from your own perspective, you also would definitely prefer to withdraw a paper as soon as possible, and definitely before it appears on the list of accepted papers (or worse, in the proceeding). Otherwise, questions may be raised about the paper that appears in the list but not presented, or worse, you will be publishing an incorrect paper. Both may  affect your reputation.

(I assume you wish to withdraw because some kind of a problem, but maybe your situation is different; in that case, you can edit your question to give more details)