Use the 3dinfo command, or the Datamode->Misc->OLay Info menu item, to display the header information about the dataset. Somewhere in there, depending on how you created the dataset, will be a listing of the statistical parameters for the correlation coefficient. There are 3 parameters, which I call nsam, nfit, and nort, which are the number of time points in the analysis, the number of regressors used for the signal, and the number of regressors of no interest (i.e., the baseline model). The denominatorial number of degrees of freedom is nsam-nfit-nort, and the numeratorial DOF is nfit. Only if these two DOF values are the same will the same r-value give the same p-value.
