Do i need to report dividends reinvested back into the 401k if I received a 1099-DIV form.

[MichaelL1]

Anything that takes place inside the retirement account does not get reflected in your return.

The only thing that matters to you is when money is put in (listed on the W-2) or when money is taken out (will then be on a 1099R). 

[BobB7]

But no 1099-DIV should have been issued, either!