Yes, you can, but you need to register the LLC in MD as a "foreign" (that is, not set up in MD) entity doing business there. This is usually very simple and straightforward: you should be able to do so directly on the MD Dept. of Assessements and Taxation website, or at least get links to forms and instructions. Here is a link that may be helpful: http://dat.maryland.gov/Pages/sdatforms.aspx