Hello:
Is it possible to execute an excel macro based on condition of a cell?

Yes. There are two ways to do it (that I can think of)

-you have an ongoing macro which automatically runs every second which checks the cells and executes your desired macro if a condition is met
-you have a routine which executes every time a change is made to the sheet which checks every cell, such as the following example:
Private Sub Worksheet_Change(ByVal Target As Excel.Range)
If Cells(1, 1) = "Hi" Then RunMeNow
End Sub
Sub RunMeNow()
MsgBox ("Hello to you too!")
End Sub

Right click on the name tab of a worksheet, select "View Code" and paste in that text. Do whatever you want on the sheet, and as soon as you enter the word "Hi" into cell A1, then the macro RunMeNow executes.

Hope that helps you

Tom