From Pandas data frame, how to get index of non "NaN" values?

My data frame is

    A    b     c
0   1    q1    1
1   2    NaN   3
2   3    q2    3
3   4    q1    NaN
4   5    q2    7

And I want the index of the rows in which column b is not NaN. (there can be NaN values in other column e.g. c )

non_nana_index = [0,2,3,4]

Using this non "NaN" index list I want to create new data frame which column b do not have "Nan"

df2=

    A    b     c
0   1    q1    1
1   3    q2    3
2   4    q1    NaN
3   5    q2    7

Just filter them

In [62]:df['b'].notnull()Out[62]:
0     True
1    False
2     True
3     True
4     True
Name: b, dtype: bool
In [63]:df[df['b'].notnull()]
Out[63]:A   b   c
0  1  q1   1
2  3  q2   3
3  4  q1 NaN
4  5  q2   7