I assume that a WordPress automatic update has occurred or a plugin or theme installation has occurred. ARQ is designed to automatically backup files and turn itself back On. See the link below.
http://forum.ait-pro.com/forums/topic/autorestore-quarantine-guide-read-me-first/#automation
If you would like to permanently turn Off ARQ and not allow any ARQ Automation then you can choose to use the AutoRestore >>> ARQ Cron Override On or Off: Default Setting is Off option and set it to: Turn On ARQ Cron Override.