Shy is the adjective describing a person who demonstrates shyness.

Shyness (also called diffidence) is the feeling of apprehension, lack of comfort, or awkwardness especially when a person is in proximity to other people. This commonly occurs in new situations or with unfamiliar people. Shyness can be a characteristic of people who have low self-esteem. Stronger forms of shyness are usually referred to as social anxiety or social phobia.