This dataset describes the mass spectrometric identification of tau phosphorylation sites in hippocampal neurons active during fear memory encoding. Tau knockout (tau‑/‑) mice were used as a background to selectively express human 2N4R tau variants in behaviourally activated neuronal populations. Tau‑/‑ mice received bilateral injections into the dorsal and ventral hippocampus with doxycycline‑regulated AAV vectors under control of the robust activity‑marking (RAM) promoter. Experimental groups expressed either wild‑type human 2N4R tau (tauWT; n = 4), a phosphorylation‑deficient tau mutant (tauT205A; n = 4), or eGFP as a negative control (n = 2). Following postoperative recovery, mice underwent fear conditioning. Hippocampal tissue was collected 120 minutes after conditioning, prior to induction of transgene expression. Temporal control of tau, tauT205A, or eGFP expression was achieved by doxycycline withdrawal, allowing expression during a defined 20‑hour window corresponding to neuronal activity associated with fear memory encoding. Tau protein was subsequently immunoprecipitated from hippocampal lysates and subjected to bottom‑up phosphoproteomic analysis. Immunoprecipitated tau was reduced, alkylated, and digested with trypsin, followed by enrichment of phosphopeptides using titanium dioxide (TiO₂) affinity chromatography. Enriched phosphopeptides were buffer‑exchanged, dried by vacuum centrifugation, resuspended, and analysed by liquid chromatography–tandem mass spectrometry (LC‑MS/MS). This dataset enables comparative analysis of tau phosphorylation patterns associated with neuronal activation during fear learning and provides insight into the role of the T205 phosphorylation site in activity‑dependent tau regulation.