My phone changed the screen to the apple logo and kind of 'reboot it self' by it self

So I was on my phone on Safari and all of a sudden , the screen freezes. I tapped it a couple times and nothing happened. Then, in a matter of a couple seconds, my iPhone 4 changes the screen to the apple logo(the black background and the apple logo in the middle, kinda like it was rebooting itself by itself. This isnt the only time this has happened , about three times total... I have iOS7 so I dont know i thats the problem or what..:/ please help thank you. ALso, i have ios 7.0.4 do I have to update it in order for it to stop?