Not out of the box, no. You'd need to use CB Auto Actions for that. Easiest way to do that for mentions is to act on the mentions trigger. The below should work.
Global
Triggers: activity_onAfterCreateActivityStreamMention
Type: Email
Access: Everybody
User: Automatic
Action
To: [var3_user_id]
Subject: You were mentioned in a post!
Body:
Code:
You were mentioned <a href="DOMAIN_HERE/index.php?option=com_comprofiler&view=pluginclass&plugin=cbactivity&action=activity&id=[var2_id]">in this post</a>.
That triggers variables are as follows.
var1 = activity stream object
var2 = activity post object
var3 = mentioned object
With CB 3.x we'll be working on a centralized notification system so users can subscribe to specific notifications for email, pms, sms, or on-site. So hopefully this will become less cumbersome to setup in future releases.