Why does the Coptic church still perform circumcisions? Circumcision is a requirement from The Mosaic Law:


  Any uncircumcised male who has not been circumcised in the flesh of
  his foreskin will be cut off from his people – he has failed to carry
  out my requirement. (Gen. 17:14, NIV)


However the old laws are no longer a requirement based on being saved by grace.


  For it is by grace you have been saved, through faith--and this is not
  from yourselves, it is the gift of God (Ephesians 2:8, NIV)


I understand that the Coptic Orthodox Church still practices circumcision. What is the Biblical basis for this?
Actually they don't; it is derived from Egyptian culture, not necessarily Christian Coptic. The Coptic Church does infant baptism as a sign of the covenant, and you should know that the Coptic Church holds to the view that the Church is the New Israel.