Active monitoring and scheduled scanning in ClamXav?
From a cursory read of ClamXav's online documentation, it appears that both of those features are available. 


For Active monitoring, ClamXav allows you to specify any number of folders to watch (e.g. your Downloads folder) as well as having a way to scan incoming email and inserted disks. 
For Scheduling scanning, there is a preference pane which allows you to both schedule virus definition updates and perform periodic scans.


I would recommend reading their online documentation.