Does the newer MacBook Pro need anti virus I am purchasing MacBook Pro 2017 with Touch Bar and I was told by one customer representative of the shop that you need anti virus because old one use to come with build in anti virus but not the new one. 

Is it true? If so why?
Sounds like a salesman is trying to make money off you...

Macs have never been supplied with a built-in antivirus - they do have active prevention in such as Gatekeeper but no 'true' antivirus app.

They have traditionally not been the target of most viruses - Windows viruses won't run on Macs, of course - though there are some threats out there. Nothing is truly safe from predators.

Full 'protection' is available from antivirus companies, just the same as for Windows. Some free, some paid. None of them is a complete guarantee.
Some will slow the machine down more than others, just the same as on Windows.

There is no absolute authority on "which antivirus is best" for any platform, but the closest thing to an authority might be AV-TEST.org. Until recently they only had very generic reports on Mac AV, but they have now started taking the testing more seriously. 

One app they don't test [lots of politics happened, not going to go into it] is Malwarebytes, which is a free 'on demand' scanner for Mac, i.e. it doesn't run constantly, only when you tell it to. It is possible to use it in conjunction with any other live-scan antivirus.
Otherwise, never have more than one AV installed on any machine - they fight each other.

Late edit: Malwarebytes v3 is now a full on-access scanner as well as on-demand.

Many many Mac users have no antivirus at all. Macs have long been believed to be, if not immune, then "not a target".
So, the final call is yours, but don't be sold something just because the salesman wants you to spend more money.
Think it over &amp; do the research before you put your hand in your pocket.