The Taliban tried the woman in a 'Shariah court' in Matta sub-district of Swat for allegedly committing adultery and found her guilty. They then asked her brother-in-law to shoot her dead in their presence.
The brother-in-law killed the woman on Sunday by spraying bullets at her, The News daily reported on Monday.
The Taliban have been running Shariah courts in areas controlled by them and punishing people with impunity. The courts have given death sentences and punished "criminals" with public flogging.
The militants also put up posters at Landi Kotal in the Khyber tribal region warning women against visiting offices of the National Database and Registration Authority to apply for identity cards.
A large number of men have been accompanying their wives to the NADRA office in the Khyber Agency to apply for identity cards so that the women can enroll for the Benazir Income Support Programme launched by the government for the poor.
Women are entitled to a monthly stipend under the programme.
The Taliban posters in bazars of Landi Kotal described the practice as "obscene" and "un-Islamic". The militants threatened the families of women applying for identity cards with "serious consequences". Local residents had earlier complained that the NADRA office did not have female staff to cater to women.
The Taliban have also continued destroying girls' schools in the Swat valley. They blew up two more girls' schools recently. Both schools were reduced to rubble by the blasts.
The militants have destroyed over 120 girls' schools in Swat and also targeted health facilities and bridges to pressure the government.
In another incident, an Afghan national was gunned down inside a mosque in Mingora, the main city of Swat district, on Sunday.