Ok, I'm going to phrase this answer in two parts because I'm not sure what you mean by clear.
-Assuming by clear you mean: the wort is finished fermenting, and I'm ready to bottle the beer.
The answer to that is. Yes. Three weeks in the primary is definitely long enough for just about any ale. Assuming your fermentation temp was warmer than 58* or so, you wort has definitely fermented out, the yeast have cleaned up all the diayctl in the wort, and almost all of them have dropped out of solution to the bottom of fermenter. Don't worry, there are still plenty of yeast in suspension to bottle condition the beer.
-Assuming you mean: will my beer be clear enough to see through
Maybe.... If you used an English or American yeast, your yeast will have dropped out of suspension, so if the beer is hazy, the yeast aren't the reason. If you're looking for clear beers, try this: After your beer is fully carbonated in the bottle, stick the bottles in the fridge for two to three weeks. They will clear up nicely.
Being that this is your third batch of beer, I wouldn't be too overly concerned with the clarity of your beer. Focus on making it taste good, and making more beer. Once you're making beer faster than you can drink it, is a good time to work on clarity issues =)
