No wood frame is archival since wood is a naturally acidic product. As mentioned in another post you do want to try to make sure there arent any bugs that will crawl over to your print. One of the advantages of the mat is that it provides a nice buffer between the edge of the print and the frame. If you dont use a mat or if you want an extra level of protection then you can use Lineco frame sealing tape.

Cheers,
Mark