I tested the following code in the Keil Simulator, and it behaved as described by the OP - ie, P1 = 10 whatever the value of 'a':

#include <REG8252.H>

void main(void)
{
	float a;

	a=5.34;

	if( a > 1.2 )
		P1=20;
	else;
		P1=10;

	while(1);
} 

It contains the typo suggested here: http://www.8052.com/forum/read.phtml?id=137189

So, presumably, the code the OP posted is not the actual code that he tested - but we'll have to wait for further information from Ajad Chhatkuli to be sure...