Solved.

The function closeEvent() is inappropriate for this case.
I just created a kinship between the windows to make this possible. The closeEvent () now comes as a complement.

Qt Code: 
  1. #!/usr/bin/env python
  2. #-*- coding: utf-8 -*-
  3.  
  4. import sys
  5. from PyQt4.QtGui import *
  6. from PyQt4.QtCore import *
  7.  
  8.  
  9. class popup(QMainWindow):
  10. 	def __init__(self,parent=None): # Parentesco
  11. 		super(popup,self).__init__(parent)
  12.  
  13.  
  14. 		self.setWindowTitle("Janela Popup")
  15.  
  16.  
  17. 		self.setMinimumSize(400 , 400)
  18.  
  19.  
  20.  
  21. class Mainw(QMainWindow):
  22. 	def __init__(self, parent=None):
  23. 		super(Mainw, self).__init__(parent)
  24.  
  25.  
  26. 		self.setMinimumSize(400 , 400)
  27.  
  28.  
  29. 		self.setWindowTitle("Janela Principal")
  30.  
  31. 		self.btn1 = QPushButton("Popup", self)
  32.  
  33. 		self.btn1.setGeometry(QRect(100, 50, 200, 200))
  34.  
  35. 		QObject.connect(self.btn1, SIGNAL("clicked()"), self.openpopup)
  36.  
  37. 	def openpopup(self):
  38. 		pop = popup(self)
  39. 		pop.show()
  40.  
  41.  
  42.  
  43. if __name__ == "__main__":
  44. 	app = QApplication(sys.argv)
  45. 	main = Mainw()
  46. 	main.show()
  47. 	sys.exit(app.exec_())
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