Hi and welcome to Just Answer!AS long as that is not your income - there should not be any tax implications.However - your friend - assuming he/she is an US citizen or US resident - might be required to report the fact of having a foreign bank account.
Your friend will need to report foreign bank account as following:
(1) completing boxes 7a and 7b on Form 1040 Schedule B - http://www.irs.gov/pub/irs-pdf/f1040sb.pdf .
(2) your friend is a subject of FBAR reporting if a foreign account value is above $10,000. The form to use is TD F 90-22.1 - this form is mailed separately. There is no tax associated with these reporting.
(3) you friend might need to file form 8938 - if your amount is more than $50,000 www.irs.gov/pub/irs-pdf/f8938.pdf - that form is attached to your tax return. The due date is the same as for your tax return. That form is required by the Foreign Account Tax Compliance Act (FATCA) to improve tax compliance involving foreign financial assets and offshore accounts.
However - the bank based on their internal policy MAY report suspicious transactions - so called Suspicious Activity Reporting (SAR) to appropriate authorities. Such reporting may include supporting documentation. Banks use a number of methods to identify potentially suspicious activity, including but not limited to activity identified by employees during day-to-day operations, law enforcement inquiries, or requests, etc. You may find more details of SAR reporting here - http://www.fincen.gov/whatsnew/pdf/20120329.pdf
Here is the SAR form - http://www.fincen.gov/forms/files/f9022-47_sar-di.pdf
You may contact your banker and provide additional information about that transaction to ensure that would not be viewed as suspicious and provide all supporting documents they might request.