Padmamma, the deceased, was found with her throat slit in her residence in Chikkabanahalli area in Kadugodi, police said.
The accused, Anandappa, a mason, was also found in an injured state in Padmamma's house with a blood-smeared knife near him, they said.
Padmamma, who had separated from her husband, was living alone and had developed an illicit relationship with Anandappa, a married man with three children, police said.
When Anandappa's wife came to know about the relationship, she used to quarrel with him, which could have resulted in Padmamma's alleged murder, they added.
However, the actual motive behind the alleged murder would be known only after interrogating Anandappa once he was fit to speak, police said.
The accused has been admitted to hospital and is stated to be out of danger, they said.
Deccan Herald is on WhatsApp Channels| Join now for Breaking News & Editor's Picks