No – unless you had a clinical deficiency of B-vitamins, which weakened your energy metabolism causing muscle wasting and/or depression. Adding B-vitamins to the deficient diet would then help you regain health and muscles, which would of course add weight that is beneficial to your health. This notion may be related to people who were partially deficient and then began taking a multivitamin and mineral formula (MVM) and subsequently added muscle/weight.
The bottom line is, B-vitamins will not cause unwanted weight gain and if you are dieting, you should always take a daily MVM to help preserve muscle.