prey (on someone's) mind

Translations
терзать (чей-либо) ум
The thought of the upcoming exam has been preying on his mind.
Мысль о предстоящем экзамене терзала его ум.
Definitions
To cause someone to worry, feel anxious, or be troubled, often persistently or repeatedly.
Words
mind

noun
ум
prey

verb
охотиться