Can a bad temper be caused by a chemical imbalence ?

Temper: Certainly! mood disorders (such as depression or bipolar), anxiety disorders, and adhd, for example, all have some biological basis to them. A bad temper can be one way these disorders present. However, a bad temper may also be part of a person's personality or due to medical problems like seizures. The most practical way to find out is to get an evaluation by your doctor and go from there.

Yes: Increased irritability is commonly associated with unipolar depression & bipolar disorder.

That's possible: You have already received two excellent responses about possible medical / chemical causes of bad temper. I just wanted to point out - that regardless of the reason for a bed temper - it is important to work on expressing ones emotions in appropriate ways.