The organisation has described the dead at Emanuel AME Church as "Satan's boyz" and warned on social networking site Twitter it would attempt to picket the funerals.
It claimed online that God sent shooter Dylann Roof, who killed the pastor Revd Clementa Pinckney, Cynthia Hurd, 54, Revd Sharonda Coleman-Singleton, 45, Tywanza Sanders, 26, Ethel Lance, 70, Revd Depayne Middleton-Doctor, 49, Susie Jackson, 87, Revd Daniel Simmons Sr, 74 and Myra Thompson, 59.
The White House has confirmed US President Barack Obama will attend the funeral of Revd Pinckney on Friday.
A number of people have also promised on social media to form a 'human barrier' around the funerals to prevent Westboro getting close to the events.
Elsewhere the hacking group Anonymous has pledged to take down the computer systems of Westboro in response to the threat.
In a statement the activists said they would "entirely" destroy the organisations online presence.
Westboro Baptist Church is based in Kansas and has around 50 members. It has found fame through picketing the funerals of soldiers or other notable people.