Some quick things that caught my attention:

* Your code does not handle exceptions, what if the user inputs "xyz" and the program raises a ValueError?

* Some PEP-8 things:
   1. A comma ```,``` should be followed by a [space], for readability;
   2. A modulo operator, as well as other mathematical operators, should be 
       preceded by and followed by a [space];
   3. A ```range()``` call (or any other function call), should **not** be followed by 
       a [space] before the first argument;

* Use ```i += 1``` instead of ```i = i + 1```;

* Calling ```print``` without ```" "``` will also print -nothing-.


Rewritten
-------------

    while True:
        x = raw_input("Input a number: ")
        try:
            x = int(x)
            break
        except ValueError:
            print("Input must be a number!")

    for i in range(x):
        a = map(int, raw_input().split())
        if a[0] == 1:
            a[0] = 2
        for num in range(a[0], a[1]+1):
            if num == 2:
                print num
            for j in range(2, num):
                if num % j == 0:
                    break
                elif j == num - 1:
                    print num
        print 
        i += 1