Butterfly bush, scientific name Buddleja davidii, is not classified as invasive in Michigan. For now, it is considered a garden escapee or a weed. You can learn more about it from the University of Michigan herbarium website. 

That said, butterfly bush is illegal to grow or sell in Oregon and Washington states. It is listed as invasive in Pennsylvania, New Jersey, and Virginia. It is listed as potentially invasive in Ohio. 

Older varieties of butterfly bush seed prolifically. That is where the problem arises. If you purchased your plant recently and purchased a cultivar that is sold as "sterile", then your plant should produce fewer seeds. 

However, if your plant is older, or it came up on its own from seed, it is not sterile and could contribute to a growing problem. 

If you want to keep it, make sure you deadhead the spent flowers before they go to seed. 

Although butterflies flock to butterfly bushes, the are not a host for the larva (caterpillars) of most of our native butterflies. You might want to consider replacing it with a native species of shrub or herbaceous plant that can both host native caterpillars and provide nectar for butterflies. 

Here are some resources from the MSU Pollinator Initiative.