Remove outliers from pandas dataframe python

It seems you need boolean indexing with ~ for invert condition, because need filter only not outliers rows (and drop outliers):

df1 = df[~df.groupby('Data').transform( lambda x: abs(x-x.mean()) > 1.96*x.std()).values]
print (df1)
       Data      Time
0 -0.704239  7.304021
1 -0.704239  7.352021
2 -0.704239  7.400021
3 -0.704239  7.448021
4 -0.825279  7.496021