frightened = feeling fear or worry.
To find the frequency of prepositions that come after the adjective frightened, we can search in iWeb corpus for:
frightened _I
We have added example sentences containing frightened preposition:
1 FRIGHTENED OF 4688
What have you got to be frightened of?
2 FRIGHTENED BY 4585
People are frightened by the way that I look, especially children.
3 FRIGHTENED AT 703
Never be frightened at your own faint heartedness in attaining love.
4 FRIGHTENED FOR 531
And there you were sitting right on the edge of the rocks and I was frightened for you.
5 FRIGHTENED ABOUT 510
6 FRIGHTENED TO 349
7 FRIGHTENED IN 327
8 FRIGHTENED INTO 249
9 FRIGHTENED OUT 213
10 FRIGHTENED FROM 101 (This is quite rare)
Not all of these are ‘correct’ uses of English.