Subconscious anxiety is anxiety that's just there. It might not be present for any obvious or particular reason. It causes an individual to feel nervous, worried or on edge throughout the day.
Many neurotypical people feel anxious about a particular circumstance. For example, a neurotypical person might be anxious about the meeting they're having with their boss later. They can feel anxious all the time leading up to the meeting, but at least they know why, and the anxiety will probably go when the meeting is over.
Autistic people (or anyone who has an anxiety disorder) may have something called 'subconscious anxiety', which means they feel anxious regardless of what is going on. If you think you experience this, or that your loved one experiences this, I hope this article helps you.