This paper focuses on the study of a stochastic model for predicting the statistical measure for time to seroconversion of HIV infected using change of parameter of antigenic diversity threshold distribution. The antigenic diversity threshold plays an important role in the determination of the expected time to seroconversion. We propose a stochastic model assuming that the intercontact times between the successive contacts are poisson random variables and the change of parameter of the threshold distribution. The mean time to seroconversion and its variance are derived and the numerical illustrations are provided.