My 3 yo daughter has started to stutter, i know this is normal for her age but when should it be a concern?

she usually does it more when she is excited or feels pressured to say whats on her mind. she is a very lively energetic little girl, so her being "excited" is usually most of the time. i have read this is normal and it has been going on for about 2 months and lately a little more than usual, should i be concerned?