Is it permissible to deposit money in a savings account that yields an annual interest of 6%?

What you have mentioned could mean two things: First, that the bank invests the funds in lawful ways, and has set for its clients a 6% profit share from the expected earnings. This is a form of permissible and lawful Mudarabah (profit-sharing). Second, that the bank invests these funds in usurious loans and deposits, or that the interest is determined from the client's capital and not from the profits. This is a forbidden act. A condition for the validity of Mudarabah is that the loss is borne by the owner of the capital and not by the worker, unless there is negligence on the worker's part.