"Although Jedi were not required to be chaste as well, many Jedi were due to sex being considered self-indulgence and an unnecessary act. At least one special case was recorded in this arrangement: Ki-Adi-Mundi who, due to low Cerean birth-rates, was permitted to have a polygamous marriage, and fathered seven daughters."
Source: http://starwars.wikia.com/wiki/Jedi under 'Way of Life'
So yeah, it's heavily frowned upon. As a roleplayer, I've met a few people who say, "So long as they don't get attached to one another, they can F* Like rabbits." To which I roll my eyes, as it's merely an excuse people make so they can play Jedi who are as one poster said, starts with the letter S and ends in T with two letters in between.