I've noticed that too. But my acquaintance from Beijing pronounces that word as "ren", not "zhen". I expressly asked her to record her pronunciation and send it to me to compare. But my Chinese teacher from my university, who is Chinese herself, seems to pronounce that word as "zhen" and she is not from Beijing. Looks like regional differences.

中国的口音主要在南北地域上差异大，并且不同省份都有差异。按照汉语标准拼音，人读作ren。你提到的zhen也许是中国古代皇帝的自称：朕。Chinese accents is differernt,and the accents between provincies is different.According to Mandarin Chinese standard prononciation,it pronounce "ren".

I think maybe you'd misheard the pronunciation. In Putonghua, 人 pronounce as 'ren /ɻən/', nnever 'zhen /tʂ/'; In some dialects, it maybe pronounces as 'yin /jin/', 'nin /ɲin/' or others. And when speaking Putonghua, sometimes people in some of these dialects pronounce 人 as '/zən/' owing to their unability to make the sound of 'r' /ɻ/, and this probably is the reason that you felt they were pronouncing the sound of 'zhen'.

"人" just pronounced as "ren". may i ask that which tv show that you heard they pronounce "zhen"? because there are 7 dialects in china, the pronounciation of dialect will effect the pronounciation of mandarin.

never heard that before but im 100% sure thats definitely wrong