suspicious of/about
what is the preposition after suspicious?

For example, in this sentence:

I'm suspicious of/about his behavior. I think he is up to something.

Question

suspicious of/about
what is the preposition after suspicious?

For example, in this sentence:

I'm suspicious of/about his behavior. I think he is up to something.

Answer

There's a subtle difference that you can use either one and use them interchangeably.
The difference:
 Use 'Suspicious Of' when you just think that not in detail. But, use 'Suspicious About' when you think but in detail. (More detailed than 'suspicious of') 
and I think that 'Suspicious Of' is used for people, while 'Suspicious About' is used for something (Not people, but their behavior, habit etc.).

Answer

Either is fine.