Depends on your needs. There's qcad
http://www.qcad.org/ which might do it for you. It does 2D, and reads and writes DXF's.
There's PythonCAD. I know much less about this one
http://www.pythoncad.org/ .
Catia is an AutoCAD competitor which does not officially support Linux, but some have gotten it to work.
And finally, people have made AutoCAD itsself work on linux via WINE
http://www.winehq.org , but this could potentially be a lot of work.