remove database mirrring

HI,

Two days back i have removed mirroring using remove mirroring option in Management option for restore the earlier backup.But when I try to restore backup its failed with error only user can be kiiled.Then I had ran Sp_who2 & checked that one system process is blocking this database & running db mirror command.

Can any one tell me is there any thing wrong from my side to remove mirroring.Why system is bloked this DB.