Polytheism is generally the belief or worship of multiple gods. 
 
We believe that many gods exist (other than The Father, the Son and the Holy Ghost) however we do not worship them, we merely acknowledge there existence.  
 
The LDS church worships one God and that is God the Father. 
 
Please remember that the term Christian is not defined in the bible, but was used only by enemies of the church in reference to the followers of Jesus Christ.  
 
Are we polytheistic? I would say not, we are merely followers of Christ, according to the dictates of our own conscience.