A is a sparse Matrix, B is a constant, how to represent a non-zero element in A is greater than B.
It is not clear what you are trying to do
You can specify A(m,n) >= B(m,n) for the combinations of m and n for which you want A to be non-zero.
Using your example at How to edit the following expression in cvx? in which the ones in a are the non-zero entries for A, you could use
A(a == 1) >= B(a == 1)