No, I think that is quite normal. All babies are different and it a lot depends on the birth weight of the baby. A baby that is born quite heavy will be much heavier at 6 weeks than a baby that was around 6/7 pounds at birth. I read somewhere that once the baby regains her birth weight, she should gain around 6 to 9 pounds a week (on average).
Tristan was nearly 10 pounds when he was born and he was 11 pounds and 2 ounces at 5 weeks! I had him weighed yesterday at 8 weeks and he weighed 12 pounds and 7 ounces.