Many Google AdSense publishers are reporting they are receiving, not one, but two checks from Google this month. The only issue is, the checks are duplicates, exact copies of each other. So technically, you can only deposit one of those checks.
If you do get a duplicate check, I would not try to deposit both. It is a bit illegal to deposit the same check twice. Yes, I know, you got two checks, but they are virtually copies of each other, so technically, you would be depositing the same check twice.