While exporting users as csv I am getting the result as json file.
The issue should have been addressed as part of this PR so on the next release of the extension this should no longer be a problem. At this time, I don’t have concrete information about when will the release containing that fix will be available, however, you can still get a CSV export if you go directly to the API; check, this other question/answer about the exact situation:
http://community.auth0.com/questions/11582/importexport-extension-is-not-working-in-csv-forma