This pattern is equivalent to the English "One is afraid that...so...". It gives cause to the resulting action or inaction.

- can be used with any verb except 이다

Examples:
눈이 내릴까 봐,따뜻한 옷을 입었어요./I was afraid it would snow, so I wore warm clothing.
효리가 집에 안 계실까 봐, 걱정했습니다./I was afraid that Hyolee wouldn't be home.