Yeah, but you'd need to get a new fork with a longer steerer tube, and a new stem, and of cours ea new headset. May be worth it, depends on the bike and what you use it for, and how much you'd be upgrading it anyway. If everything currently on the bike is in good working condition, not really worth it. Would be worth it if you planned to upgrade the fork anyway, for example.
Also, most bikes with threadless systems have 1 1/8" headtube, while most bikes with quill stems have 1" headtube. However, threadless and threaded headsets are available on both sizes. If your bike has a 1" headtube (which is a good guess since it's threaded currently), your selection of forks is more limited. But there's enough.