Yes, if the document type you use provides for math. The mathematics-using community is developing software, and there is a MathML proposal at the W3C, which is a native XML application. It would also be possible to make XML fragments from the long-expired HTML3, HTML Pro, or ISO 12083 Math, or OpenMath, or one of your own making. Browsers which display simple math embedded in SGML already exist (eg Panorama, Multidoc Pro).
If you want to learn more about MathML, you can read the article: MathML - What's in it for us?