You may have received the MFA One-Time Access Code via email, mobile phone or automated voice message because someone you shared your Online Banking User ID and Password with has attempted to login to Online Banking.
This could be your spouse or a company you've requested to do something on your behalf. Perhaps you registered at a website that will pull all of your account information into one location. Or perhaps you signed up for an ACH transfer, new direct deposit, electronic tax refund, signed up for bill pay, etc. If you did and you provided your Online Banking credentials, that company could be trying to verify that the account is actually yours.
If you don't recall doing any of these things, please let us know ASAP so we can investigate further.