在某人的后面，可以用英语表示为：

He is behind me.
He is at my back.

其中，behind是一个介词，表示在某人或某物的后面。at my back则是一个介词短语，也表示在某人的后面。

举例：

I felt someone tap me on the shoulder, and when I turned around, I saw that he was behind me.
我感觉有人在我肩膀上轻轻地拍了一下，当我转过身时，我发现他就在我后面。

I heard footsteps behind me, and when I turned around, I saw that he was at my back.
我听到了身后的脚步声，当我转过身时，我发现他就在我后面。