Technically, if you are doing the surveys to earn money, then you have a 'profit motive' and it is self-employment income. Self-employment income should be reported on Schedule C and the related self-employment taxes paid on it.
However, if taking surveys is something you like to do for fun or enjoyment and you receive money for taking them, the income can be classified as Hobby Income, which gets reported as Miscellaneous Income on your 1040.