If there is fraudulent activity found on a business bank account (C corporation) can the business owner be personally held responsible?

The short answer is yes, maybe.  Ultimately, here are different ways the owner can be held personally liable:

1. Ultra Vires/Piercing the Corporate Veil -- if the activities render the corporation just a name and really the activities of the owner in a fraudulent manner, then the court will go past the corporate structure (pierce the corporate veil) and render the owner and/or directors personally liable.

2. Commingling the account into a personal account or personal uses.

3. If the company requires licensure in a state or with the federal government, oftentimes there are provisions in each state it is licensed that call for separate liability of each principal (which includes owners, executive officers, etc.).