incrediBILL - 12:59 am on Mar 27, 2012 (gmt 0)

Probably not in Apache itself.

However, you could set a cron job that executes every 1-5 minutes and calls a script that checks to see if error_log has changed and send an email if it has.

Not sure I'd want this because if a bad bot hits your site testing vulnerabilities it can easily clutter up error_log with errors that don't really exist and send a lot of worthless email in a hurry.