It's possible that a small scab in a straight line on your lip could be due to herpes, particularly if you've had cold sores before. Herpes simplex virus (HSV) can cause outbreaks of blistering lesions that then crust over and form scabs as they heal. However, it's also important to consider other factors like injury or even dry skin that may have caused the small scab. If you're unsure about whether it's related to herpes, consulting with a healthcare provider for proper evaluation and testing would be advisable just to rule out any potential concerns.