jakebohall - 8:06 pm on May 21, 2013 (gmt 0)
This could easily happen if you are using get parameters to generate the page with the filters applied.
If you already have a dedicated brand page, this could create duplicate content issues (not good). If this is the case, then you should consider no-indexing the brand filter page, adding a canonical to the brand pages if brand filter is applied, or using the options available in Google Webmaster Tools. (http://support.google.com/webmasters/bin/answer.py?hl=en&answer=1235687)