“心不在焉”常见的英文表达有 “absent-minded”、“inattentive” 或 “distracted”，具体使用可根据语境和侧重点来选择：
Absent-minded：侧重于描述一个人因注意力分散或精神不集中，而显得心不在焉、健忘的状态。例如：He's so absent-minded that he often forgets his keys.（他总是心不在焉，经常忘记带钥匙。）
Inattentive：强调对周围事物或他人不够关注、不注意，常用于描述对某件事或某个人缺乏应有的注意力。例如：The students were inattentive during the lecture.（学生们在听讲座时心不在焉。）
Distracted：指因外界干扰或内心思绪而分散了注意力，导致无法专注于当前任务或情况。例如：She was too distracted by her phone to hear what I was saying.（她被手机分心，没听到我在说什么。）