The IRS confirmed that some economic impact payments were indeed sent by mistake to nonresident aliens, incarcerated people, and deceased taxpayers. Pursuant to IRS guidelines and CARES Act, these individuals were not eligible for stimulus checks (see this link).

The IRS now asking those recipients, or their family members, to return the money. While the IRS hasn’t outlined any consequences for not returning a stimulus check it sent by mistake, the newly released guidance says you “should” return the money “immediately.” It is unclear what repercussions a failure to return the money may have on future immigration benefits applications, so we would encourage all individuals on F, J, or B visas or who filed their last tax return as non-resident aliens to check with their CPA if they qualify for the stimulus checks and if not to promptly return the funds. We also recommend carefully documenting the return of funds and keeping copy of proof of reimbursement.

Please see link with instructions on how to return the funds to the IRS:
https://www.irs.gov/taxtopics/tc161