A mutual fund is an investment vehicle ... instead of owning one stock you own a portion of a portfolio being managed professionally. Now you can own the mutual fund in an ordinary broker's account or a retirement plan like an IRA. Only you can know where the fund is being housed. And investing in a mutual fund is not a tax deduction itself ... however if you made an IRA contribution then that may be deductible.
you can own a mutual fund that is not part of a retirement plan. in such case you are taxed on any income that is reported on 1099's (1099-div, 1099-B) from that fund. on the other hand you can have a mutual fund that is held by a retirement plan. its earnings would not be taxable to you (you would not receive a 1099-div or 1099-B). if you put money in (made a contribution) , it could be tax deductible if it is not a contribution to a ROTH retirement account. if you took money out it could be taxable - you would get a 1099-R.
you have provided no details about the account so all that can be offered is generalities. however, you can call the mutual fund to get more information as to what you have.