Yes. If you have taken classes at another university and are transferring to the Freie Universität, or if you have completed classes during your stay abroad, you can receive credit points to count toward your BA degree. The content of the courses has to fit your BA curriculum, i.e. if your fields of concentration are, for instance, Political Science, Sociology, and History, you will have difficulties receiving credit for a class on literature. Please also keep in mind that the subject of your studies is North America. See here for detailed information on the procedure and the necessary forms.