The Oregon Master Naturalist Program offers an online course, which is required to become a full Oregon Master Naturalist. Information about the online course, including cost, can be found at http://pne.oregonstate.edu/course/oregon-master-naturalist-online
This online course is offered through Oregon State University's Professional and Non-credit Education program, and is offered twice a year, in the winter or spring and fall. Exact dates will be posted here when they are available.
Click here for further details on how to become an Oregon Master Naturalist.