class Principal(QMainWindow):
    def __init__(self):
        QMainWindow.__init__(self)
        uic.loadUi("nuev.ui",self)

        self.menuBar().installEventFilter(self)

    def eventFilter(self, obj, event):
        if obj is self.menuBar() and event.type() == QEvent.MouseMove:
            return True
        return QMainWindow.eventFilter(self, obj, event)


if __name__ == '__main__':
    import sys

    app = QApplication(sys.argv)
    p = Principal()
    p.show()
    sys.exit(app.exec_())