See the little bright the little dot in the picture bellow? It's Earth taken by the Mars Curiosity Rover's left eye camera called Mastcam. The image was taken on Jan 31, 2014, about 80 minutes after Martian sunset.
The distance between Mars and Earth in the time Curiosity took the shot was about 160 million kilometers (99 million miles). If you were standing on Mars, you would see Earth and the moon without any problem as two bright starts in the sky. For more information and high resolution images, click here.