According to the NHS Choices website
'Anxiety is a feeling of unease, such as worry or fear, that can be mild or severe. Everyone experiences feelings of anxiety at some point in their life. For example, you may feel worried and anxious about sitting an exam or having a medical test or job interview.'
However research shows that many people on the autism spectrum are more anxious than other people.
Sometimes the anxiety is caused by underlying issues such as sensory sensitivities. Sometimes the anxiety is made worse by specific events, such as a stranger entering the room.