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)
Select custom and click next
In the select items for backup dialog box select add items and select the system state and click ok.
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.