Here are some examples of how "un-" can be used to create words with a similar meaning:
* Unsuspecting: not expecting or anticipating something, unaware
* Unprepared: not ready for something, lacking anticipation
* Unforeseen: not expected or anticipated, coming as a surprise
* Unwary: lacking caution, easily deceived
It's important to note that "unsuspecting" is a complete word in itself, and doesn't require a prefix to convey its meaning.