That depends on whether or not you plan on harvesting it for medicinal purposes. If you harvest just as it's going to flower, you should be able to keep it in check.

Mugwort will spread aggressively by underground stolons as well. It can really take over an area! I would confine mugwort to its own bed or area. Then, be attentive to plucking out strays - and follow those stolons underground. Often, they will be more than 2 foot away from the plant from whence it sprang.