Cash it at your own risk. I used to work in payroll for a huge company and I can think of two instances where a bonus went to wrong person. If the check wasn't supposed to go to you and you cash it, they will find out and try to get the money back. My advice would be to inquire about why got the check, because you won't get to keep the money (if you want to keep your job) if you weren't supposed to get it in the first place.

In one of the instances I was talking about above two employees had the same name and the wrong one got an $80,000 bonus. By the time the right person came around asking where his 80 grand was, the other guy wasn't with the company anymore. They didn't try to recover the $80K because it wasn't worth it (I told you it was a huge company).

Unfortunately, no one at the place (who was due a huge bonus) had the same name as me.