Why do I keep thinking I see someone in the corner of my eye?

Peripheral vision is good at noticing movement but less clear about details, so a shadow or passing shape can briefly look person-like. Lighting, reflections, and things at the edge of your view can add to that. If it stops once you look directly, that may be one ordinary explanation.

Since it happens in several places, I’d keep a simple note of when it occurs and what was going on, like poor lighting, tiredness, or a headache. If this is new, becoming more frequent, or worrying you, consider arranging an eye exam or talking with a healthcare professional.

Pay attention to any other changes in your vision too. New flashes of light, a sudden increase in floaters, or a dark shadow over part of your sight deserve prompt medical attention. If none of that is happening but the episodes keep recurring, a routine check is still a reasonable next step.