Why did I receive a tax refund check this month with no explanation why I received it?

[bushnj00]

2018 income tax return was successfully filed before the deadline earlier this year.  I have no reason to expect a refund check.  I owed and I paid it.

[rjs]

Is it a federal refund? You will probably get a letter from the IRS a week or two after you got the check, explaining why they sent the refund. They send the checks out before the letters.