Ground state electron configuration of chromium
WebElements page about chromium (and a number of resources) agree with the comment by @Philipp:


  The ground state electron configuration of ground state gaseous neutral chromium is  $\ce{[Ar]}3d^54s^1$


Which in some resources is written as $\ce{[Ar]}4s^13d^5$



Based on the Royal Society of Chemistry article The trouble with the aufbau principle:


  it appears that the most stable configuration for atoms of chromium, copper, niobium, molybdenum, ruthenium, rhodium, silver, platinum and gold involves only moving one electron into an $s$ orbital.


Chromium is one of a handful of Transition elements that share this electron configuration.