There are nobody in the room. Don't be afraid.

There is nobody in the room.

像anybody something nobody这一类的词叫做不定代词
不定代词后的谓语动词要用单数

nobody
anybody
everybody

连接前缀都都用is修饰

分离前缀给据意思有些用are
比如说
All people
Some body
等

There is nobody in the room.

PS：nobody.anybody,somebody作主语动词用单三.....

把 are 改成 is

are改为is