There are two ways to do an Active Directory Backup natively. The first is Windows Server Backup and the second is WBADMIN.

Before you use windows server backup you need to install the Windows Server Backup feature

 

Open Windows Server Backup from the tools menu.

you can choose a local or online backup (I am demonstrating local)

Click Next

Select custom and click next

In the select items for backup dialog box select add items and select the system state and click ok.

Click next

Select a schedule that suits your environment and click next

Select a destination that suits you and click next

If your backup destination it not showing click Show all available Disks

Select the one you want and click Ok.

Select the correct backup disk and click next

At the conformation screen click finish

the Scheduled task can be viewed in Task Scheduler

or with wbadmin

wbadmin start systemstatebackup -backupTarget:d:

You could put that in a batch file and schedule it.