As of 2015 there is no conclusive evidence that life on Mars exists or has ever existed, but scientists are hesitant to give a definitive answer without conclusive data. Most experts agree that it is theoretically possible that Mars could have life, but without evidence there is no way to know for certain.
There is some scientific controversy around this question. In 1996, NASA announced that scientists had recovered a Martian rock that fell to earth, which had fossilized evidence of microbial life. While there were both fervent supporters and skeptics, more research was performed and fewer experts agreed that the rock contained fossils.
There are other areas of research that suggest that Mars may once have sustained life. In 2014, NASA announced that its Curiosity rover, which worked to gather geographical and geological data on Mars, had found evidence of methane gas on Mars. The methane would appear in spikes, which led scientists to believe that it was potentially being produced by a life form.