Disable command history in a windows batch file

Short answer

doskey /reinstall

This erases the complete history.

A second way could also to start a new cmd.exe instance in your batch, this would only remove the history made by your set/p statements.

@echo off
if "%~1"==":historySafe" goto :historySafe
cmd /c "%~f0" :historySafe
exit /b

:historySafe
set /p var=Password
echo %var%
exit /b